literature search truncation

Search the Literature: Tips and Tricks

• Searching with Subject Headings
• Searching with keywords
• Subject Headings vs Keywords
• Boolean operators

What is truncation?

• Subheadings
• Limits (Filters)
• Pulling it all together

Truncation is the act or process of shortening or reducing something. In the context of literature searching, it refers to the shortening of a search term so as to bring up words that share a root word but have different endings. Truncation is a technique frequently used in keyword searching, in which it helps reduce the number of variations you have to search on separately.

For example:

In most databases, the truncation symbol is the asterisk (*), though it may be any character designated by the database. Check the database's Help pages for details.

A related technique is the use of wildcards , in which a character (often the asterisk) may be substituted for zero or more letters within the interior of a word. It is useful in the case of alternative spellings, e.g., tumo*r, to bring up both tumor and tumour. Again, check the database's Help pages for details.

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Database Search Tips: Truncation

• Boolean operators
• Keywords vs. subjects

What to look for

• Root words that have multiple endings.  Example: sun = suns, sunshine, sunny, sunlight
• Words that are spelled differently, but mean the same thing.  Example:  color, colour
• Truncation/wildcard symbols vary by database.  Check the help screens to find out which symbols are used.

About truncation and wildcards

Truncation :

Truncation, also called stemming, is a technique that broadens your search to include various word endings and spellings.

• To use truncation, enter the root of a word and put the truncation symbol at the end.
• The database will return results that include any ending of that root word.
• Examples: child* = child, childs, children, childrens, childhood genetic* = genetic, genetics, genetically
• Truncation symbols may vary by database; common symbols include: *, !, ?, or #

Similar to truncation, wildcards substitute a symbol for one letter of a word.

• This is useful if a word is spelled in different ways, but still has the same meaning.
• Examples: wom!n = woman, women colo?r = color, colour

If you have questions about applying this technique to your search, Ask Us!

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How truncation, wildcards, stemming and lemmatization help your literature search

By Carol Hollier on 20-Dec-2021 09:30:00

Any good search is built on the “right” search terms—terms that retrieve literature relevant to the question under investigation.

But the English language is tricky. Many variations of a word can capture a single concept. If a researcher writes one version in their article title or abstract and you search with another, you can miss relevant—and important—articles. On the other hand, in some databases you may type one word in the search box, but get results with different, albeit related, words.

What accounts for these results? What is the best way to navigate search interfaces to get the results you need?

Four processes—truncation, wildcards, stemming and lemmatization—can expand what you type to capture more versions of that term. Truncation and wildcards are simple modifications you incorporate into a term you type. Stemming and lemmatization are algorithmic adjustments built into a database platform. Knowing how they work, and how you work them, gives you an easy way improve your literature searches.

Ways you can make your search more comprehensive

The main way a researcher can optimize their search is with truncation. Wildcards are helpful, too. In each of these methods, you type some of your search term’s letters and combine those letters with symbols that stand in for the possibility of letters you are not actually typing.

What is truncation?

To truncate a search term, you type the starting letters, or stem, of a word followed by a designated symbol, such as *, $, or !.

When the truncation symbol is added to a stem, the database brings back any results that match the letters you typed plus any results that have more letters following on from what you typed. For example, results for toxin* could include toxin, toxins, toxinogenesis, toxinogenic, toxinotype, toxinotypes, toxinotyping, toxinfective, toxinaemia, and toxinometer.

Truncating a search term is a powerful way to expand a search.

How do you know which symbol to use for truncation?

The truncation symbol is often an asterisk (*). Some databases use a dollar sign ($) instead, and at least a couple of databases use an exclamation point (!). Instructions on how to truncate terms can be found in every database’s help section.

The truncation symbol will always follow the letters you have typed with no space between letters and symbol.

Which databases let you truncate search terms?

Truncation is a universal database search technique. If it doesn’t seem to be working for you, check that you are using the correct truncation symbol for that database.

How do you know where to truncate a term?

If you are not sure how many letters you should be typing to capture your term and its variations without getting too many irrelevant results, experiment with truncating your term at different points. It’s usually worth trying a shorter stem than you think you need in case you are surprised by the relevant results you see. If you are flooded by irrelevant results, make your stem a little longer.

Some databases limit how short a truncated stem can be. PubMed, for instance, requires four typed letters before you can truncate a term.

Can you limit how many letters can follow your truncated stem?

Sometimes. On the Ovid platform, typing adult$1 returns results with adult and adults, but not adultery or adulteration. Typing adult$3 returns results with adult, adults, and adultery, but still not adulteration. Most platforms, however, do not offer this option.

A database’s help pages detail its truncation symbols’ exact functionality.

Can you truncate the beginning of a word?

Some database platforms do let you truncate both ends of a word. In these databases, typing *toxin* would return toxin, toxins, aflatoxin, aflatoxins, ochratoxin, ochratoxins, and many more results containing the string toxin somewhere in them.

Wildcards are symbols inserted into the middle of words.[1] They allow you to span spelling variations. Some databases use different symbols for what they term mandatory and optional wildcards. Mandatory means a letter, any letter, must stand in for the symbol; optional means that any letter might stand in for the symbol, but no letter might, too. For instance on the Ovid platform, you capture both the British and American spellings of organisation/organization by typing organi#ation, but favourite/favorite are captured with favo?rite.

Ways a database platform might be making your search more comprehensive

Some database platforms aim to make our searching lives easier by building in some automated extensions of search terms. They may search for both US and UK spellings of words regardless of which you type. They may also employ algorithms for stemming and lemmatization to broaden your searches.

Stemming is an automatic process in which the database searches for the word you type, the stem of that word, plus that stem with other possible endings. So, if you search asked , stemming would be the reason why you see results not just with asked, but also with ask, asks, and asking in them.

Lemmatization cleverly identifies the lemma, or lexical root, of a typed word, and goes out to find results with the different word versions tied to that root. Imagine we type grew into our search field. Grew is the past tense of grow. Lemmatization of grew brings you both grew and grow, but also growing and grown. Similarly, a database that is lemmatizing terms would take a search for mouse and bring back some results with mouse and some with mice.

If your search returns results which are the product of stemming or lemmatization and it’s not helpful, you can generally override it by typing your search term inside quotation marks (eg. “mouse” ) to stipulate that only results containing exactly what you typed are returned.

It’s important to note that although stemming and lemmatization somewhat extend your results net, they are not the same thing as truncation. Stemming and lemmatization both work within predefined boundaries. Truncation returns any word that fits the rules you set. Stemming toxin returns toxin and toxins. Truncating toxin* returns toxin and toxins, plus toxinaemia, toxinogenic, toxinogenics, toxinotyping, toxinotypes, toxin-3α-glucoside, toxinogenesis, etc.

It’s also important to know that while lemmatization overlaps slightly with the function of a database thesaurus, it is much more limited than a thesaurus.

Lemmatization is only based on linguistic connections between words, while the thesaurus pulls together terms based on scientific usage that often goes well beyond dictionary usage. Lemmatization, for instance, would not collate bovine, heifer, cows, oxen, steers, bulls, and calves with cattle, nor BCAA with branched-chain amino acids. The FSTA thesaurus would.

Not all database platforms incorporate automated extensions of your search terms. Some only incorporate it in certain search modes. A quick way to check if what you are typing is being changed or taken literally is to sort your results by date rather than relevance. To make the check even quicker, restrict your sample search to the title field so you do not need to open records to spot which words are being captured with what you typed.

Preset algorithms in a search interface can help you find the research information you need. If you grasp the limitations of these algorithms, however, and are able take matters into your own hands by truncating terms or using wildcards, you can significantly improve your searches.

The better you understand the tools you use to find research literature, the better a job you’ll do at building powerful, efficient, and effective searches.

-------------------------------- [1] Some database platforms call all symbols, wherever they are inserted into a word, wildcards.  If you can’t find truncation in a database’s help section, look at what they say about wildcards.

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Search Tips: Truncation and Boolean Searching: Home

Truncation: what is it.

Truncation is also known as wildcard searching.  It lets you search for a term and variant spellings of that term. 

To truncate a search term, do a  keyword  search in a database, but remove the ending of the word and add an asterisk (*) to the end of the word. The database will retrieve results that include every word that begins with the letters you entered. 

BOOLEAN SEARCHING

For more precise searching, connect your keywords in a meaningful way using the words  AND ,  OR , and  NOT .

Think of these connecting words as a bridge between keywords or concepts which allows you  to  narrow  or  broaden   your search. 

The more keywords you connect with AND, the fewer results you will retrieve. The database will need to find each of your keywords in the text in order to show it to you.

For example:  "homeless youth" and education and "new york city"

Be careful not to add unnecessary words to  AND  searches. You might miss pertinent information. Sometimes the simpler the search, the better.

Here we are less picky with what terms we want to retrieve. Using OR is also helpful when we are searching for a concept that is described equally well by more than one term.

For example:  cars OR automobiles

                       environment AND (water OR lake* OR river* OR stream*)

Here the first search is asking for all information pertaining to cars or automobiles.

The second search is a little more detailed, but more precise.

This type of search is good to use when you already know what you DO NOT want. Let's say you are doing a search on new cars but you are only interested in American made models.

For example:  (cars OR automobiles) NOT Europe.

GOOD, BETTER, BEST

Good: 

• nurse AND education
• advertising AND children
• genetic engineering AND ethics
• nurs* AND education
• advertis* AND child*
• gene* engineering AND ethic*
• nurs* AND (educat* OR train* OR school*)
• (advertis* OR market*) AND (child* OR adoles*)
• gene* AND (alter* OR engineer*) AND (ethic* OR moral*)

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Advanced Search Techniques

Truncation & wildcards.

Truncation  uses an asterisk ( * ) or other symbols such as    !, ?, or # to search for multiple forms of the same root word. (Look for the database help page if you are unsure what symbols it uses.) For example:

• Searching gentrif* will find results that include gentrification , gentrifying , and gentrified   

A  wildcard  is a symbol that takes the place of an unknown character or set of characters. Commonly used wildcards are the asterisk ( * ) and the question mark ( ? ). (Look for the database help page if you are unsure what symbols it uses.)

The question mark represents only one unknown character. For example:

• Searching the word   wom?n   will have results that include   women  and   woman .

The asterisk can represent more than one character. For example:

• If you didn't know whether the spelling was color or colour, searching colo*r will search both spellings.

Truncation Example

The  Jstor  search pictured below is intended to find sources that discuss illustrated editions of Alice's Adventures in Wonderland ,  illustrat*   is used to search for sources that include  illustrate ,  illustration , illustrator , illustrating, and  illustrated.

Wildcard Example

In this International Political Science Abstracts example pictured below, a wildcard is being used because of the difference between the American spelling, labor , and the British spelling, labour . By using the wildcard both versions will be searched.

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How to Search the Literature (Advanced)

• Purpose of this Guide
• Formulate a Research Question
• Identify Search Concepts
• Identify Search Terms
• Truncation and Wildcards
• Boolean Operators
• Select a Resource to Search
• Search a Database
• Translate a Search Strategy
• Manage Search Strategies and Results
• Find the Full Text within McMaster Libraries' Collection
• Find the Full Text on a Journal's Website
• Find the Full Text Through the Interlibrary Loans Service
• Find Conference Proceedings Abstracts
• Find the Full Text to Non-English Literature

Truncation and wildcards can be applied to a keyword search in a database or search engine to broaden your results and allow you to look for variations of words.

The truncation symbol can be used in a keyword search to retrieve alternate word endings

• e.g. surg* will retrieve surgery, surgeries, surgeon, or surgical
• e.g. stud* will retrieve study, studies, student, students, etc.
• Ovid Databases  (e.g. Medline, Embase, AMED, PsycINFO) truncation symbol is an asterisk (*) or dollar sign ($)
• EBSCO Databases  (e.g. CINAHL, SPORTDiscus, Social Science Index) truncation symbol is an asterisk (*)
• PubMed  truncation symbol is an asterisk (*)
• Web of Science  truncation symbol is an asterisk (*)
• Check the help screen of other databases to find out which symbols are used

Wildcards are symbols that can optionally replace a single letter in a word

• This is useful when dealing with variant spelling (e.g. pediatric and paediatric)
• e.g. p?ediatric will return results with paediatric or pediatric
• EBSCO Databases  wildcard is the question mark (?)  or   hash tag (#)
• Web of Science  wildcard is the dollar sign ($) or question mark (?)
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Research Process

• Brainstorming
• Explore Google This link opens in a new window
• Explore Web Resources
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• Reading a Scientific Article
• Website Evaluation
• Article Keywords and Subject Terms
• Cited References
• Citing Articles
• Related Results
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• Literature Gap and Future Research
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• Annual Reviews
• Systematic Reviews & Meta-Analyses
• Finding Seminal Works
• Exhausting the Literature
• Finding Dissertations
• Researching Theoretical Frameworks
• Research Methodology & Design
• Tests and Measurements
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Truncation lets you search for a word that could have multiple endings. The symbol for truncation is usually an * at the point where the spelling of the word could change. For example, PTSD AND music* would find articles with the terms PTSD and music/musical/musician/musicians/musicality in them. Truncation is very useful when you know one of your search terms has several endings, but all of the variations represent basically the same idea. Using truncation will help you complete your search faster because you will not have to manually type in and search every variation of the word.

Wildcard Symbols

There are several wildcard symbols that can be used in several databases, such as EBSCOHost and ProQuest, to enhance your search string. 

Asterisk wildcard (*) - Is used between words where variations may be possible. Example:  "responsibility * budgeting" can return results such as, " responsibility-centered budgeting" or " responsibility center budgeting"

Question mark wildcard (?) - Is used to replace an unknown character. Example: wom ? n will return results for women or woman

See the links below to learn more about these symbols in specific databases. 

• EBSCOHost Wildcard and Truncation Symbols
• Gale Academic OneFile Wildcard Characters
• ProQuest Wildcards and Truncation

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Conducting a Literature Review

• Getting Started
• Developing a Question
• Searching the Literature
• Identifying Peer-Reviewed Resources
• Managing Results
• Analyzing the Literature
• Writing the Review

Need Help? Ask Your librarian!

Search Strategies

• Boolean Operators

Once you have identified the key concepts of your research question (see "Developing a Question"), you can use those concepts to develop keywords for your search strategy. The following tips and techniques will help you design a precise and relevant search strategy.

Keywords are any words you might use to search the record of an article, book, or other material in library databases. The database searches through the metadata (such as title, authors, publication, abstract, etc.) to find resources that contain the word you searched, and may also search through the full text of the material.

Keywords are most successful when you're searching for the words that the authors use to describe the research topic, as most databases will search for those specific words within the record of the article. To increase your chance of returning relevant results, consider all of the words that  might  be used to describe the research you're trying to find, and try some of these out in sample searches to determine which words return the best results.

Search Tips - Keywords

• Search for singular and plural terms together: (physician OR physicians)
• Search for both the American and British spelling of words: (behavior OR behaviour)
• Search for synonyms of terms together: (teenager OR adolescent)
• Search for phrases inside of quotation marks: ("young adult")

Use Boolean operators to combine keywords for more precise search results. 

AND - If the term must be included in your search:

influenza AND vaccine

OR - If terms are interchangeable, i.e. synonyms. Place OR'd terms within parentheses:

(influenza OR flu) AND vaccine

NOT - If a term should not be included in your search. This Boolean operator is rarely necessary for literature reviews.

(influenza OR flu) AND vaccine NOT H1N1

Note how we've used parentheses in the examples above. Search strings like these are similar to mathematical equations, where you perform the actions within the parentheses before proceeding from left to right to run the search. For example, using the search [(influenza OR flu) AND vaccine] will find results that have a term relating to influenza/flu, as well as the term vaccine.

If we moved the parentheses, it would be a very different search. [influenza OR (flu AND vaccine)] will provide results that use the term influenza, as well as results that use both the terms flu and vaccine. This means you would get results having to do with influenza but perhaps nothing to do with vaccination. 

Here are a few examples of how this search would be different depending on the arrangement of booleans and keywords. The area highlighted in pink represents the search results that would be returned with this search.

Truncation allows you to quickly include all variations of a word in your search. Use the root of the keyword and add an asterisk (*). For example:

nurs* = nurse, nurses, nursing, nursery

IMPORTANT: Notice that "nursery" is also retrieved in the above search. Truncation will save you from having to include a large number of synonyms, but it will also add a certain number of irrelevant results. You can limit this effect by using the NOT Boolean operator, i.e. NOT nursery.

Wild cards allow you to replace a letter in a keyword to retrieve all variations of the spelling. For example:

p?ediatric = pediatric, paediatric

Free-Text vs. Thesaurus Searching

While you can search any word as a keyword, databases also contain an official list of the terms they use to describe the subject of each article, called Subject Headings. You can look up Subject Headings in the thesaurus of the database, using the thesaurus's search box to pull up the recommended Subject Heading for a given keyword. When searching specifically for Subject Headings, the database will only search the Subject Headings field within the record of each article (ie, not the title, abstract, etc.). This is a much more targeted method of searching, and is an excellent addition to your search strategy. 

A strong search strategy will use both free-text (keyword) searching and thesaurus searching, to ensure that all relevant articles have been retrieved by the search. The lists below outline the strengths and weaknesses of both types of search strategies.

Free-Text Searching

• Natural language words describing your topic
• More flexible search strategy - can use any term in any combination
• Database looks for keywords anywhere in the record - not necessarily connected together
• May yield too many or too few results
• May yield many irrelevant results

Thesaurus Searching

• Pre-defined "controlled vocabulary" words used to describe the content of each item in a database
• Less flexible search strategy - need to know the exact controlled vocabulary term
• Database looks for subjects only in the subject heading or descriptor field, where the most relevant words appear
• If too many results, you can use subheadings to focus on one aspect of a broader topic
• Results are usually very relevant to the topic

MIT Libraries. Database Search Tips: Keywords vs. Subjects. https://libguides.mit.edu/c.php?g=175963&p=1160804

Each database has their own thesaurus. You will need to adapt your search strategy for each database to take advantage of their unique thesaurus.

PubMed uses MeSH terms (Medical Subject Headings). You can learn more about finding and using MeSH terms here:

• The Basics of Medical Subject Headings (MeSH) in MEDLINE/PubMed: A Tutorial

CINAHL uses CINAHL Headings. You can learn more about finding and use these terms here:

• Using CINAHL/MeSH Headings

In other databases, look for a link with the terms "headings", "subject headings", or "thesaurus" to find the appropriate thesaurus terms for your search.

Citation Searching

Citation searching is a search strategy that allows you to search either forward or backwards time through the literature based on an identified relevant article:

You can search forward in time by using databases that allow you to search for other articles that have cited the identified relevant article. (Web of Science and Google Scholar can do this automatically.)

• Web of Science (Clarivate Analytics)
• Google Scholar

You can search backward in time by reviewing the reference list of the identified relevant article for additional article citations.

For more information about how to perform citation searches, check out this guide from the University of Toledo Libraries:

• How To: Cited Reference Searches in Web of Science Guide from the University of Toledo

Retrieving Materials

Select a database.

When searching for articles, it is best to use an appropriate subject database rather than the SearchIT catalog. Be sure to select your database from the Spokane Academic Library homepage to ensure that you will have access to full-text articles.

"Find It @ WSU" Button in PubMed

When you have found an article that you would like to read in its entirety, look for the "Find It @ WSU" Button. This button will take you to the article entry in the SearchIT catalog.

Here's what that looks like in PubMed.

"Find It @ WSU" Button in CINAHL

"Find It @ WSU" Button in PsycINFO

Accessing the Full-Text Article

After selecting the "Find It @ WSU" Button, you will be taken to the article entry in SearchIT. Select the link under the Access Options box to be directed to the full-text article. 

If an article is not available in the WSU Libraries collection, you can request the article through interlibrary loan by selecting the link under "Access Options".

See the Using Interlibrary Loan section for more information.

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Best Practice for Literature Searching

• Literature Search Best Practice
• What is literature searching?
• What are literature reviews?
• Hierarchies of evidence
• 1. Managing references
• 2. Defining your research question
• 3. Where to search
• 4. Search strategy
• 5. Screening results
• 6. Paper acquisition
• 7. Critical appraisal
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Creating a search strategy

Once you have determined what your research question is and where you think you should search, you need to translate your question into a useable search. Doing so will:

• Make it much more likely that you will find the relevant research and minimise false hits (irrelevant results)
• Save you time in the long run
• Help you to stay objective throughout your searching and stick to your plan
• Help you replicate and update your results (where needed)
• Help future researchers build on your research.

If you need to explore a topic first, your search strategy can initially be quite loose. You can then revisit search terms and update your search strategy accordingly. Record your search strategy as you develop it and capture the final version for each place that you search.

Remember that information retrieval in the area of food is complex because of the broadness of the field and the way in which content is indexed.   As a result, there is often a high level of ‘noise’ when searching food topics in a database not designed for food content. Creating successful search strategies involves knowledge of a database, its scope, indexing and structure.

• Key concepts and meaningful terms
• Keywords or subject headings
• Alternative keywords
• Care in linking concepts correctly
• Regular evaluation of search results, to ensure that your search is focused
• A detailed record of your final strategy. You will need to re-run your search at the end of the review process to catch any new literature published since you began.
• Search matrix
• Populated matrix
• Revised matrix (after running searches)

• DOWNLOAD THE SEARCH MATRIX

Using a search matrix helps you brainstorm and collect words to include in your search. To populate a search matrix:

• Identify the main concepts in your search
• Run initial searches with your terms, scanning abstract and subject terms (sometimes called descriptors, keywords, MeSH headings, or thesaurus terms, depending on which database you are using) of relevant results for words to add to the matrix.
•  Explore a database thesaurus hierarchy for suitable broader and narrower terms.

Note : You don’t need to fill all of the boxes in a search matrix.

You will find that you need to do some searches as you experiment in running it and this will help you refine your search strategy. For the search on this example question:

• Some of the broader terms turned out to be too broad, introducing a host of irrelevant results about pork and chicken
• Some of the narrower terms were unnecessary, as any result containing “beef extract” is captured by just using the term beef.

See the revised matrix (after running searches) tab!

This revised matrix shows both adjustments made to terms, and how the terms are connected with Boolean operators.  Different forms of the same concept (the columns) are connected with OR, and each of the different concepts are connected with AND.   

Search tools

• Boolean operators
• Phrases and proximity searching
• Truncation and wildcards

Boolean operators tell a database or search engine how the terms you type are related to each other.  

Use OR to connect variations representing the same concept . In many search interfaces you will want to put your OR components inside parentheses like this: (safe OR “food safety” OR decontamination OR contamination OR disinfect*). These are now lumped together into a single food safety concept for your search.

Use AND to link different concepts. By typing (safe OR “food safety” OR decontamination OR contamination OR disinfect*) AND (beef OR “cattle carcasses”)—you are directing the database to display results containing both concepts.

NOT  eliminates all results containing a specific word.  Use NOT with caution. The term excluded might be used in a way you have not anticipated, and you will not know because you will not see the missing results.

Learn more about using Boolean operators:  Research Basics: Using Boolean Operators to Build a Search (ifis.org)

The search in the matrix above would look like this in a database:

("food safety"  OR  safety  OR  decontamination  OR  contamination  OR  disinfection)  AND  (thaw*  OR  defrost*  OR  "thawing medium")  AND  ("sensory quality attributes"  OR  "sensory perception"  OR  quality  OR  aroma  OR  appearance  OR  "eating quality"  OR  juiciness  OR  mouthfeel  OR  texture  OR  "mechanical properties"  OR  "sensory analysis"  OR  "rheological properties")  AND  (beef  OR  "cattle carcasses")

Thesaurus terms will help you capture variations in words and spellings that researchers might use to refer to the same concept, but you can and should also use other mechanisms utilised by databases to do the same. This is especially important for searches in databases where the thesaurus is not specialised for food science.

• Phrase searching , putting two or more words inside quotation marks like “food safety” will ensure that those words appear in a single field (i.e. title or abstract or subject heading) together as the phrase. Phrase searching can eliminate false hits where the words used separately do not represent the needed concept.
• Some databases allow you to use proximity searching to specify that words need to be near each other. For instance, if you type ripening N5 cheese you will get results with a maximum of five words between ripening and cheese .  You would get results containing cheese ripening as well as results containing ripening of semi-hard goat cheese .

Learn how to test if a phrase search or a proximity search is the better choice for your search:  Proximity searching, phrase searching, and Boolean AND: 3 techniques to focus your literature search (ifis.org)

Note : Proximity symbols vary from database to database. Some use N plus a number, while others use NEAR, ADJ or W. Always check the database help section to be sure that you are using the right symbols for that database .

Truncating a word mean typing the start of a word, followed by a symbol, usually an asterisk (*).  This symbol tells the database to return the letters you have typed followed either by no letters (if appropriate) or letters.  It is an easy way to capture a concept that might be expressed with a variety of endings. 

Sometimes you need to adjust where you truncate to avoid irrelevant results.  See the difference between results for nutri* or nutrit*

Inserting  wildcard  symbols into words covers spelling variations.  In some databases, typing  organi?ation  would return results with  organisation  or  organization , and  flavo#r  would bring back results with  flavor  or  flavour .  

Note : While the truncation symbol is often *, it can also be $ or !.   Wildcard symbols also vary from database to database. $ or ? are sometimes used. Always check the database help section to be sure that you are using the right symbols for that database.

In building a search you can combine all the tools available to you.    “Brewer* yeast”  , which uses both phrase searching and truncation, will bring back results for  brewer yeast ,  brewer’s yeast  and  brewers yeast , three variations which are all used in the literature.

Best Practice!

BEST PRACTICE RECOMMENDATION:   Always check a database's help section to be sure that you are using the correct  proximity, truncation or wildcard symbols for that database. 

Handsearching

It is good practice to supplement your database searches with handsearching . This is the process of manually looking through the table of contents of journals and conferences to find studies that your database searches missed. A related activity is looking through the reference lists of relevant articles found through database searches. There are three reasons why doing both these things is a good idea:

• If, through handsearching, you identify additional articles which are in the database you used but weren’t included in the results from your searches, you can look at the article records to consider if you need to adjust your search strategy. You may have omitted a useful variation of a concept from your search string.
• Even when your search string is excellent, some abstracts and records don’t contain terms that allow them to be easily identified in a search, but are relevant to your research.
• References might point to research published before the indexing began for the databases you are using.

For handsearching, target journals or conference proceedings that are clearly in the area of your topic and look through tables of contents. Sometimes valuable information within supplements or letters is not indexed within databases.

Academic libraries might subscribe to tools which can speed the process such as Zetoc  (which includes conference and journal contents) or Browzine (which only covers journals).  You can also see past and current issues’ tables of contents on a journal’s webpage.

Handsearching is a valuable but labour-intensive activity, so think carefully about where to invest your time.

Best practice!

BEST PRACTICE RECOMMENDATION:   Ask a colleague, lecturer, or librarian to review your search strategy. This can be very helpful, especially if you are new to a topic. It adds credibility to your literature search and will help ensure that you are running the best search possible.

BEST PRACTICE RECOMMENDATION:   Remember to save a detailed record of your searches so that you can run them shortly before you are ready to submit your project to see if any new relevant research has been published since you embarked on your project. A good way to do this is to document:

• Where the search was run
• The exact search
• The date it was run
• The number of results

Keeping all this information will make it easy to see if your search picks up new results when you run it again.

BEST PRACTICE RECOMMENDATION: If you are publishing your research, take note of journals appearing frequently in your search results for an indication of where to publish a research topic for good impact.

• << Previous: 3. Where to search
• Next: 5. Screening results >>
• Last Updated: Sep 15, 2023 2:17 PM
• URL: https://ifis.libguides.com/literature_search_best_practice

• Subject guides
• Researching for your literature review
• Develop a search strategy

Researching for your literature review: Develop a search strategy

• Literature reviews
• Literature sources
• Before you start
• Keyword search activity
• Subject search activity
• Combined keyword and subject searching
• Online tutorials
• Apply search limits
• Run a search in different databases
• Supplementary searching
• Save your searches
• Manage results

Identify key terms and concepts

Start developing a search strategy by identifying the key words and concepts within your research question. 

For example:   How do s t udents view inclusive educational practices in schools ?

Treat each component as a separate concept (there are usually between 2-4 concepts).

For each concept list the key words derived from your research question, as well as any other relevant terms or synonyms that you have found in your preliminary searches. Also consider singular and plural forms of words, variant spellings, acronyms and relevant index terms (subject headings).  

As part of the process of developing a search strategy, it is recommended that you keep a master list of search terms for each key concept. This will make it easier when it comes to translating your search strategy across multiple database platforms. 

Concept map template for documenting search terms

Combine search terms and concepts

Boolean operators are used to combine the different concepts in your topic to form a search strategy. The main operators used to connect your terms are AND and OR . See an explanation below:

• Link keywords related to a single concept with OR
• Linking with OR broadens a search (increases the number of results) by searching for any of the alternative keywords

Example: perspective  OR attitude

• Link different concepts with AND
• Linking with AND narrows a search (reduces the number of results) by retrieving only those records that include all of your specified keywords

Example: inclusive education  AND student perspective

• using NOT narrows a search by excluding certain search terms
• Most searches do not require the use of the NOT operator

Example: education  NOT higher education  will retrieve all results that include the word education  but don’t contain the phrase  higher education .

See the website for venn diagrams demonstrating the function of AND/OR/NOT:

Combine the search terms using Boolean

Advanced search operators - truncation and wildcards

Use symbols to retrieve word variations:

The truncation symbol is commonly an asterisk * and is added at the end of a word.

• The asterisk applied to the root of a word captures other endings to that root word making it useful for retrieving singular, plural and other variations of a keyword.

Example:  educat *  will retrieve educat ion, educat ors, educat ional , etc

Note: If you don't want to retrieve all possible variations, an easy alternative is to utilise the OR operator instead e.g. education OR educational.

The wildcard symbols include the question mark ? and hash #. They replace zero, one or more characters in the middle of a word.

Example:  wom # n finds woman or women, behavio ? r finds behaviour or behavior.

The symbols may vary in different databases - See the Database search tips guide for details or check the Help link in any database.

Phrase searching

Use quotes to keep word order when searching for phrases.

For phrase searching, place two or more words in "inverted commas" or "quote marks".

Example: “inclusive education”

In some databases, words may be searched separately if the quote marks are not used. In other databases, word order may be maintained without the need for quote marks.

See the Database search tips for details on phrase searching in key databases, or check the Help link in any database.

Subject headings (index terms)

Identify appropriate subject headings (index terms).

Many databases use subject headings to index content. These are selected from a controlled list and describe what the article is about. 

A comprehensive search strategy is often best achieved by using a combination of keywords and subject headings where possible.

In-depth knowledge of subject headings is not required for users to benefit from improved search performance using them in their searches.

Advantages of subject searching:

• Helps locate articles that use synonyms, variant spellings, plurals
• Search terms don’t have to appear in the title or abstract

Note: Subject headings are often unique to a particular database, so you will need to look for appropriate subject headings in each database you intend to use.

Subject headings are not available for every topic, and it is best to only select them if they relate closely to your area of interest.

Create a gold set

It is useful to build a ‘sample set’ or ‘gold set’ of relevant references before you develop your search strategy.  .

Sources for a 'gold set' may include:

• key papers recommended by subject experts or supervisors
• citation searching - looking at a reference list to see who has been cited, or using a citation database (eg. Scopus, Web of Science) to see who has cited a known relevant article
• results of preliminary scoping searches.

The papers in your 'gold set' can then be used to help you identify relevant search terms

• Look up your 'sample set' articles in a database that you will use for your literature review. For the articles indexed in the database, look at the records to see what keywords and/or subject headings are listed.

The 'gold set' will also provide a means of testing your search strategy

• When an indexed article is not retrieved, your search strategy can be revised in order to include it (see what concepts or keywords can be incorporated into your search strategy so that the article is retrieved).
• If your search strategy is retrieving a lot of irrelevant results, look at the irrelevant records to determine why they are being retrieved. What keywords or subject headings are causing them to appear? Can you change these without losing any relevant articles from your results?

Example search strategy

An example of a search strategy incorporating all three concepts that could be applied to different databases is shown below:.

The above search strategy in a nested format (for use in a single search box) would look like:

(student* OR pupil* OR "young people" OR learner*) AND (perception* OR experience OR voice OR perspective*) AND (inclusi* OR "special education" OR belonging OR disabilit*)

• << Previous: Search strategies - Education/Social sciences topic example
• Next: Keyword search activity >>

Literature Search

• First Online: 16 November 2022

Cite this chapter

• Mourouguessine Vimal 4  

1009 Accesses

Literature search is one of the most daunting tasks, especially for the novice researchers. However, it is one of the most essential steps in the research process and every researcher should know the various literature search techniques in order to develop the skill of performing a quick and effective literature search. Literature search refers to gathering information in a systematic manner from various published and non-published literature sources. This chapter discusses the different types of medical literature like primary, secondary and tertiary literature. It also discusses about the two broad types of literature search like physical literature exploration and electronic literature search. Also, the various steps involved in performing a literature search including the various techniques to improve literature search like MeSH term search, phrase search, field search, use of Boolean operators, wildcard search and truncation search have also been elucidated in this chapter.

• Literature review
• Keyword search
• Boolean operators
• MeSH search

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Bibliography

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Literature Search. In: Raveendran R, Gitanjali B, Manikandan S, editors. A practical approach to PG dissertation. 2nd ed. Hyderabad: PharmaMed Press; 2012. p. 21–9.

Mansoor I. Tips on searching the internet for medical information. J Family Community Med. 2002 Jan;9(1):57–61.

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Vimal, M. (2022). Literature Search. In: Lakshmanan, M., Shewade, D.G., Raj, G.M. (eds) Introduction to Basics of Pharmacology and Toxicology. Springer, Singapore. https://doi.org/10.1007/978-981-19-5343-9_55

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Literature Search Basics

Develop a search strategy.

• Define your search
• Decide where to search

What is a search strategy

Advanced search tips.

• Track and save your search
• Class Recording: Writing an Effective Narrative Review
• A search strategy includes  a combination of keywords, subject headings, and limiters (language, date, publication type, etc.)
• A search strategy should be planned out and practiced before executing the final search in a database.
• A search strategy and search results should be documented throughout the searching process.

What is a search strategy?

A search strategy is an organized combination of keywords, phrases, subject headings, and limiters used to search a database.

Your search strategy will include:

• keywords 
• boolean operators
• variations of search terms (synonyms, suffixes)
• subject headings 

Your search strategy  may  include:

• truncation (where applicable)
• phrases (where applicable)
• limiters (date, language, age, publication type, etc.)

A search strategy usually requires several iterations. You will need to test the strategy along the way to ensure that you are finding relevant articles. It's also a good idea to review your search strategy with your co-authors. They may have ideas about terms or concepts you may have missed.

Additionally, each database you search is developed differently. You will need to adjust your strategy for each database your search.  For instance, Embase is a European database, many of the medical terms are slightly different than those used in MEDLINE and PubMed.

Choose search terms

Start by writing down as many terms as you can think of that relate to your question. You might try  cited reference searching  to find a few good articles that you can review for relevant terms.

Remember than most terms or  concepts can be expressed in different ways.  A few things to consider:

• synonyms: "cancer" may be referred to as "neoplasms", "tumors", or "malignancy"
• abbreviations: spell out the word instead of abbreviating
• generic vs. trade names of drugs

Search for the exact phrase

If you want words to appear next to each other in an exact phrase, use quotation marks, eg “self-esteem”.

Phrase searching decreases the number of results you get. Most databases allow you to search for phrases, but check the database guide if you are unsure.

Truncation and wildcards

Many databases use an asterisk (*) as their truncation symbol  to find various word endings like singulars and plurals.  Check the database help section if you are not sure which symbol to use. 

"Therap*"

retrieves: therapy, therapies, therapist or therapists.

Use a wildcard (?) to find different spellings like British and American spellings.

"Behavio?r" retrieves behaviour and behavior.

Searching with subject headings

Database subject headings are controlled vocabulary terms that a database uses to describe what an article is about.

Using appropriate subject headings enhances your search and will help you to find more results on your topic. This is because subject headings find articles according to their subject, even if the article does not use your chosen key words.

You should combine both subject headings and keywords in your search strategy for each of the concepts you identify. This is particularly important if you are undertaking a systematic review or an in-depth piece of work

Subject headings may vary between databases, so you need to investigate each database separately to find the subject headings they use. For example, for MEDLINE you can use MeSH (Medical Subject Headings) and for Embase you can use the EMTREE thesaurus.

SEARCH TIP:  In Ovid databases, search for a known key paper by title, select the "complete reference" button to see which subject headings the database indexers have given that article, and consider adding relevant ones to your own search strategy.

Use Boolean logic to combine search terms

Boolean operators (AND, OR and NOT) allow you to try different combinations of search terms or subject headings.

Databases often show Boolean operators as buttons or drop-down menus that you can click to combine your search terms or results.

The main Boolean operators are:

OR is used to find articles that mention  either  of the topics you search for.

AND is used to find articles that mention  both  of the searched topics.

NOT excludes a search term or concept. It should be used with caution as you may inadvertently exclude relevant references.

For example, searching for “self-esteem NOT eating disorders” finds articles that mention self-esteem but removes any articles that mention eating disorders.

Adjacency searching 

Use adjacency operators to search by phrase or with two or more words in relation to one another. A djacency searching commands differ among databases. Check the database help section if you are not sure which searching commands to use. 

In Ovid Medline

"breast ADJ3 cancer" finds the word breast within three words of cancer, in any order.

This includes breast cancer or cancer of the breast.

Cited Reference Searching

Cited reference searching is a method to find articles that have been cited by other publications. 

Use cited reference searching to:

• find keywords or terms you may need to include in your search strategy
• find pivotal papers the same or similar subject area
• find pivotal authors in the same or similar subject area
• track how a topic has developed over time

Cited reference searching is available through these tools:

• Web of Science
• GoogleScholar
• << Previous: Decide where to search
• Next: Track and save your search >>
• Last Updated: Nov 29, 2022 3:34 PM
• URL: https://mdanderson.libguides.com/literaturesearchbasics

Strategies for searching and managing evidence-based practice resources

• PMID: 25221988
• DOI: 10.3928/00220124-20140916-01

Evidence-based nursing practice requires the use of effective search strategies to locate relevant resources to guide practice change. Continuing education and staff development professionals can assist nurses to conduct effective literature searches. This article provides suggestions for strategies to aid in identifying search terms. Strategies also are recommended for refining searches by using controlled vocabulary, truncation, Boolean operators, PICOT (Population/Patient Problem, Intervention, Comparison, Outcome, Time) searching, and search limits. Suggestions for methods of managing resources also are identified. Using these approaches will assist in more effective literature searches and may help evidence-based practice decisions.

Copyright 2014, SLACK Incorporated.

• Education, Nursing, Continuing / organization & administration*
• Evidence-Based Nursing / organization & administration*
• Information Storage and Retrieval
• Nursing Informatics / organization & administration*
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• Staff Development / organization & administration*
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• Indian J Anaesth
• v.60(9); 2016 Sep

Literature search for research planning and identification of research problem

Anju grewal.

Department of Anaesthesiology, Dayanand Medical College and Hospital, Ludhiana, Punjab, India

Hanish Kataria

1 Department of Surgery, Government Medical College and Hospital, Chandigarh, India

2 Department of Cardiac Anaesthesia, All India Institute of Medical Sciences, New Delhi, India

Literature search is a key step in performing good authentic research. It helps in formulating a research question and planning the study. The available published data are enormous; therefore, choosing the appropriate articles relevant to your study in question is an art. It can be time-consuming, tiring and can lead to disinterest or even abandonment of search in between if not carried out in a step-wise manner. Various databases are available for performing literature search. This article primarily stresses on how to formulate a research question, the various types and sources for literature search, which will help make your search specific and time-saving.

INTRODUCTION

Literature search is a systematic and well-organised search from the already published data to identify a breadth of good quality references on a specific topic.[ 1 ] The reasons for conducting literature search are numerous that include drawing information for making evidence-based guidelines, a step in the research method and as part of academic assessment.[ 2 ] However, the main purpose of a thorough literature search is to formulate a research question by evaluating the available literature with an eye on gaps still amenable to further research.

Research problem[ 3 ] is typically a topic of interest and of some familiarity to the researcher. It needs to be channelised by focussing on information yet to be explored. Once we have narrowed down the problem, seeking and analysing existing literature may further straighten out the research approach.

A research hypothesis[ 4 ] is a carefully created testimony of how you expect the research to proceed. It is one of the most important tools which aids to answer the research question. It should be apt containing necessary components, and raise a question that can be tested and investigated.

The literature search can be exhaustive and time-consuming, but there are some simple steps which can help you plan and manage the process. The most important are formulating the research questions and planning your search.

FORMULATING THE RESEARCH QUESTION

Literature search is done to identify appropriate methodology, design of the study; population sampled and sampling methods, methods of measuring concepts and techniques of analysis. It also helps in determining extraneous variables affecting the outcome and identifying faults or lacunae that could be avoided.

Formulating a well-focused question is a critical step for facilitating good clinical research.[ 5 ] There can be general questions or patient-oriented questions that arise from clinical issues. Patient-oriented questions can involve the effect of therapy or disease or examine advantage versus disadvantage for a group of patients.[ 6 ]

For example, we want to evaluate the effect of a particular drug (e.g., dexmedetomidine) for procedural sedation in day care surgery patients. While formulating a research question, one should consider certain criteria, referred as ‘FINER’ (F-Feasible, I-Interesting, N-Novel, E-Ethical, R-Relevant) criteria.[ 5 ] The idea should be interesting and relevant to clinical research. It should either confirm, refute or add information to already done research work. One should also keep in mind the patient population under study and the resources available in a given set up. Also the entire research process should conform to the ethical principles of research.

The patient or study population, intervention, comparison or control arm, primary outcome, timing of measurement of outcome (PICOT) is a well-known approach for framing a leading research question.[ 7 , 8 ] Dividing the questions into key components makes it easy and searchable. In this case scenario:

• Patients (P) – What is the important group of patients? for example, day care surgery
• Intervention (I) – What is the important intervention? for example, intravenous dexmedetomidine
• Comparison (C) – What is the important intervention of comparison? for example, intravenous ketamine
• Outcome (O) – What is the effect of intervention? for example, analgesic efficacy, procedural awareness, drug side effects
• Time (T) – Time interval for measuring the outcome: Hourly for first 4 h then 4 hourly till 24 h post-procedure.

Multiple questions can be formulated from patient's problem and concern. A well-focused question should be chosen for research according to significance for patient interest and relevance to our knowledge. Good research questions address the lacunae in available literature with an aim to impact the clinical practice in a constructive manner. There are limited outcome research and relevant resources, for example, electronic database system, database and hospital information system in India. Even when these factors are available, data about existing resources is not widely accessible.[ 9 ]

TYPES OF MEDICAL LITERATURE

(Further details in chapter ‘Types of studies and research design’ in this issue).

Primary literature

Primary sources are the authentic publication of an expert's new evidence, conclusions and proposals (case reports, clinical trials, etc) and are usually published in a peer-reviewed journal. Preliminary reports, congress papers and preprints also constitute primary literature.[ 2 ]

Secondary literature

Secondary sources are systematic review articles or meta-analyses where material derived from primary source literature are infererred and evaluated.[ 2 ]

Tertiary literature

Tertiary literature consists of collections that compile information from primary or secondary literature (eg., reference books).[ 2 ]

METHODS OF LITERATURE SEARCH

There are various methods of literature search that are used alone or in combination [ Table 1 ]. For past few decades, searching the local as well as national library for books, journals, etc., was the usual practice and still physical literature exploration is an important component of any systematic review search process.[ 10 , 11 ] With the advancement of technology, the Internet is now the gateway to the maze of vast medical literature.[ 12 ] Conducting a literature review involves web-based search engines, i.e., Google, Google Scholar, etc., [ Table 2 ], or using various electronic research databases to identify materials that describe the research topic or those homologous to it.[ 13 , 14 ]

Methods of literature search

Web based methods of literature search

The various databases available for literature search include databases for original published articles in the journals [ Table 2 ] and evidence-based databases for integrated information available as systematic reviews and abstracts [ Table 3 ].[ 12 , 14 ] Most of these are not freely available to the individual user. PubMed ( http://www.ncbi.nlm.nih.gov/pubmed/ ) is the largest available resource since 1996; however, a large number of sources now provide free access to literature in the biomedical field.[ 15 ] More than 26 million citations from Medline, life science journals and online books are included in PubMed. Links to the full-text material are included in citations from PubMed Central and publisher web sites.[ 16 ] The choice of databases depends on the subject of interest and potential coverage by the different databases. Education Resources Information Centre is a free online digital library of education research and information sponsored by the Institute of Education Sciences of the U.S. Department of Education, available at http://eric.ed.gov/ . No one database can search all the medical literature. There is need to search several different databases. At a minimum, PubMed or Medline, Embase and the Cochrane central trials Registry need to be searched. When searching these databases, emphasis should be given to meta-analysis, systematic reviews randomised controlled trials and landmark studies.

Electronic source of Evidence-Based Database

Time allocated to the search needs attention as exploring and selecting data are early steps in the research method and research conducted as part of academic assessment have narrow timeframes.[ 17 ] In Indian scenario, limited outcome research and accessibility to data leads to less thorough knowledge of nature of research problem. This results in the formulation of the inappropriate research question and increases the time to literature search.

TYPES OF SEARCH

Type of search can be described in different forms according to the subject of interest. It increases the chances of retrieving relevant information from a search.

Translating research question to keywords

This will provide results based on any of the words specified; hence, they are the cornerstone of an effective search. Synonyms/alternate terms should be considered to elicit further information, i.e., barbiturates in place of thiopentone. Spellings should also be taken into account, i.e., anesthesia in place of anaesthesia (American and British). Most databases use controlled word-stock to establish common search terms (or keywords). Some of these alternative keywords can be looked from database thesaurus.[ 4 ] Another strategy is combining keywords with Boolean operators. It is important to keep a note of keywords and methods used in exploring the literature as these will need to be described later in the design of search process.

‘Medical Subject Heading (MeSH) is the National Library of Medicine's controlled hierarchical vocabulary that is used for indexing articles in PubMed, with more specific terms organised underneath more general terms’.[ 17 ] This provides a reliable way to retrieve citations that use different terminology for identical ideas, as it indexes articles based on content. Two features of PubMed that can increase yield of specific articles are ‘Automatic term mapping’ and ‘automatic term explosion’.[ 4 ]

For example, if the search keyword is heart attack, this term will match with MeSH transcription table heading and then explode into various subheadings. This helps to construct the search by adding and selecting MeSH subheadings and families of MeSH by use of hyperlinks.[ 4 ]

We can set limits to a clinical trial for retrieving higher level of evidence (i.e., randomised controlled clinical trial). Furthermore, one can browse through the link entitled ‘Related Articles’. This PubMed feature searches for similar citations using an intricate algorithm that scans titles, abstracts and MeSH terms.[ 4 ]

Phrase search

This will provide pages with only the words typed in the phrase, in that exact order and with no words in between them.

Boolean operators

AND, OR and NOT are the three Boolean operators named after the mathematician George Boole.[ 18 ] Combining two words using ‘AND’ will fetch articles that mention both the words. Using ‘OR’ will widen the search and fetch more articles that mention either subject. While using the term ‘NOT’ to combine words will fetch articles containing the first word but not the second, thus narrowing the search.

Filters can also be used to refine the search, for example, article types, text availability, language, age, sex and journal categories.

Overall, the recommendations for methodology of literature search can be as below (Creswell)[ 19 ]

• Identify keywords and use them to search articles from library and internet resources as described above
• Search several databases to search articles related to your topic
• Use thesaurus to identify terms to locate your articles
• Find an article that is similar to your topic; then look at the terms used to describe it, and use them for your search
• Use databases that provide full-text articles (free through academic libraries, Internet or for a fee) as much as possible so that you can save time searching for your articles
• If you are examining a topic for the first time and unaware of the research on it, start with broad syntheses of the literature, such as overviews, summaries of the literature on your topic or review articles
• Start with the most recent issues of the journals, and look for studies about your topic and then work backward in time. Follow-up on references at the end of the articles for more sources to examine
• Refer books on a single topic by a single author or group of authors or books that contain chapters written by different authors
• Next look for recent conference papers. Often, conference papers report the latest research developments. Contact authors of pertinent studies. Write or phone them, asking if they know of studies related to your area of interest
• The easy access and ability to capture entire articles from the web make it attractive. However, check these articles carefully for authenticity and quality and be cautious about whether they represent systematic research.

The whole process of literature search[ 20 ] is summarised in Figure 1 .

Process of literature search

Literature search provides not only an opportunity to learn more about a given topic but provides insight on how the topic was studied by previous analysts. It helps to interpret ideas, detect shortcomings and recognise opportunities. In short, systematic and well-organised research may help in designing a novel research.

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