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Medical Literature Searching

A step by step guide to the literature searching process & techniques

Welcome

What is a Literature Search?

A literature search is a planned & organized search for relevant literature on a specific topic. Writing a review of the existing literature on a topic is key part of research conducted in medicine. Literature searches are conducted using databases, library catalogues, & the internet. Literature searching requires time, planning & knowledge of database searching techniques.

Remember that searching:

  • is an ITERATIVE process
  • often requires re-evaluation and testing. You may need to add or change keywords & adjust for the ways they relate to each other or consider choosing new resources to search or even reword or change the research question!
  • requires an understanding of the trade-off between search precision & sensitivity
  • is very interesting once you learn how to do it!

This guide will provide you with

  • steps & techniques to help you search more effectively
  • an understanding of thesaurus & keyword searching
  • an understanding of some advanced search techniques

Literature Search: Process Flow

The process of writing a literature review involves the following steps:

 

Define your question. Is it Feasible, Interesting, Novel, Ethical, & Relevant?

Formulate your search using keywords, thesaurus terms & boolean logic strategy.

Select relevant databases & other internet sources to search

Start  your search; keep track of your results from each database. 

 Evaluate your results  & refine your search terms & logic if necessary based on relevancy of results to your question.

Literature Search Steps

Define your search question 

Start by Identifying a broad topic & consider whether it is Feasible, Interesting, Novel, Ethical, & Relevant. 

Example: You are interested in understanding prostate cancer diagnosis. You know that a PSA test is one way of diagnosing it. You want to find out how effective this test is as a diagnostic tool.

Turn your topic into a question; a clearly-defined question will:

  • focus your search to make it more efficient & effective
  • make it easier to find & combine appropriate search terms
  • help you identify relevant & irrelevant results 

What is your topic stated as a question: ''Does the PSA test effectively diagnose prostate cancer?''

 

Formulate your search  A concept table may help you gather terms for your search. Use it to:

  • Brainstorm a list of synonyms &/or phrases for each different concept  in your question. 
  • Also include correct thesaurus terms used by the database you have chosen.

PICO questions

The PICO method helps you derive an answerable question  to focus your search for resources on your topic of interest..

Once  you have thought about your concepts & some related keyword, & formulated an answerable question, you are ready to choose a database.

You may also wish to consider different question formulations which may be better suited to your research topic: 

PICOST (Like PICO but with additional areas to consider): Population, Intervention, Comparison, Outcome, Situation, Type of Study
PICOT:  Population,  Intervention, Comparison,  Outcome, Time Frame
PEO: Population and/or Problem, Exposures, Outcome
PCCPopulation, Concept, and Context [often used in Scoping Reviews]
PESTEL: Political, Economic, Social, Technological, Environmental and Legal Factors
SPICE: Setting, Population or Perspective, Intervention, Comparison, Evaluation
ECLIPS [management & service related issues]: Expectations, Client Group, Location, Impact, Professionals Involved, Service
MIP [medical ethics review]: Methodology, Issues, Participants
SPIDER: Sample, Phenomenon of interest, Design, Evaluation, Research type 

For full details, please see

Booth, A. et al. (2019) Formulating questions to explore complex interventions within qualitative evidence synthesis.

Do i need only a few results or many results?

Specific or Sensitive Search. Which one do i need?

The number, type & combination of terms you use in your search will depend on both your question & the objective of your research.  A search can not be both specific & sensitive. Your job as a researcher is to find the balance.

A specific search  (also called precise or narrow search)

  • requires a specific answer, is most likely clear & easily described with keywords &/or thesaurus terms.
    • e.g. What is the recommended daily dose of paracetamol for a child with fever?
  •  may be one where you only need a few articles on a specific topic
    • e.g. use of flipped classroom techniques in medical education to stimulate student participation in lectures or you want  a recent RCT on the effectiveness of diclofenac for osteoarthritis
A specific search will retrieve very relevant results, but not all relevant papers will be found.

 A sensitive search (also called a broad search)

  • requires researcher to gather all relevant literature  & includes the most recent evidence which may not yet have thesaurus term assigned;  
    • e.g. find all studies on the influence of diet on Rheumatoid arthritis from the last 10 years for a Systematic Review you wish to publish
  • it may include concepts that do not have precise thesaurus terms & may require combinations of synonyms to capture all aspect of your research question.
    • e.g. you are doing PhD research & you are worried about missing any relevent studies
A sensitive search is less precise & will retrieve a combination of relevant & less relevant results which you will need to include or exclude according to your question.

Tips to increase sensitivity or precision

 Tips to increase Sensitivity

  • refine question or objective
  • remove concept from your search    

               -  instead of CANCER and CHEMOTHERAPY and NAUSEA --> search CHEMOTHERAPY and

             NAUSEA instead

  • search more synonyms for each concept in your question (find the outliers!)

                - instead of CHEMOTHERAPY and NAUSEA --> search (chemotherapy OR alemtuzumab OR  

             cisplatin OR Hexalen) AND (nausea OR vomiting OR emesis)

  • search more than 1 database

 

Tips to increase Precision

  • refine question or objective
  • add a concept to your search, or combine two concepts into one

             - instead of TYLENOL and FEVER --> search TYLENOL and FEVER and RANDOMIZED

             - instead of CHEMOTHERAPY and NAUSEA --> search ''CHEMOTHERAPY INDUCED NAUSEA AND

               VOMITING''

  •  restrict search words to title, title/abstract, or author-provided keywords
  •  use tools of the database to restrict search results to only those where your concept is the MAJOR SUBJECT of the article
  • use study filters, date limits, or clinical queries to restrict results of the search
  • use different sort options to force more relevant or higher cited articles to the top of your results (in some databases)
  • search a distilled information resource, such as BMJ Best Practice instead of a database

Recording your search strategies & saving results

Literature searches often produce a large number of citations & require use of several databases.

Good search practice includes keeping a search diary or a document including details of your search strategy to allow others to reproduce your steps & get the same results.

Record your search strategies by logging details on

  •  all database & any other sources you search - eg Medline, Cochrane Library, Google Scholar, etc.
  • note down journal titles that appear often during your searches to familiarize yourself with prominent journals in your area of interest.                 
  • which search terms you used (keyword, subject headings,words and phrases)                    
  • any search techniques you applied (truncation, proximity, etc)
  •  how you combined your search terms (AND/OR/NOT)
  •  the number of search results from each source & each strategy used.

Download the citations you have retrieved to a reference manager &/or excel spreadsheet to deduplicate citations if necessary.

Database Search Techniques

Why would i use a database?

Databases allow you to do different kinds of searches.

Basic keyword search: similar to a library catalogue or Google search where you use whatever keywords you think describe your topic.

Subject heading search:  use the thesaurus terms (also known as controlled vocabulary) of the database to find all articles tagged with specifically assigned subject headings.

Combined keyword & subject heading search:  for advanced research, use combined searching  to ensure retrieval of current and relevant  resources to support your research.  Start with your own basic keywords as concepts but also find out what the thesaurus term in the database is for that concept and combine them. 

Free text vs Thesaurus or MeSH searching

Using both Keyword  & Thesaurus terms in a database search will help you in the following ways.

Using a Database Thesaurus

About Thesaurus Terms:  A database thesaurus or controlled vocabulary is an index used to assign subject information to the research articles contained in database. The main thesaurus used in Medicine is called MeSH (Medical Subject Headings). MeSH is an index of medical terms used by specific databases  to classify all medical research.  When searching databases always check to see which controlled vocabulary is used. For detailed understanding of MeSH, follow this MEDLINE/PubMed Medical Subject Heading  tutorial.

Learn more about searching with subject headings on different databases

Database 

Subject Vocabulary

Subject Search Tutorials

Medline Complete & Cinahl MeSH / Cinahl Headings

 

https://youtu.be/eJJPp9yAIoA

Cochrane Library MeSH

https://youtu.be/HLD7w63rqB0

PsycInfo

Thesaurus of

Psychological

Index terms

https://youtu.be/IiW7rBBNdDg

PubMed MeSH https://youtu.be/o6CTfdx85ys
SCOPUS  No thesaurus https://youtu.be/uEHSnUh0Mag

 

Combining search terms in your search strategy with AND / OR

Once you have formulated your question, isolated your concepts & decided on your keywords &/or  thesaurus terms, combining terms is the next step:

How to combine terms for best results: use boolean operators AND,  OR,  NOT

  • AND  - all terms must be present. Used when you want to combine different concepts to find articles that include both concepts.

venn and   

 

 

 

  • OR  - either of the terms must be present. Use when you want to combine similar concepts  or  combine  several synonyms keywords and the equivalent subject heading

      

  • NOT - terms excluded from search. Use after you have combined terms using AND/OR for cases when you get many results and you wish to eliminate an unwanted subset from your results: e.g.(animals AND cloning) NOT sheep.

Using Truncation & Wildcards for Keyword Searching

When you use keywords to augment your search strategy, databases have advanced tricks to save you time & help you include as many related terms as possible.Always check database help for symbols used.

Truncation for Keyword Searching is a search technique where possible word endings are replaced by a symbol. The database will search for all possible variations of the word.

Frequently used truncation symbols include the asterisk (*), a question mark (?) or a dollar sign ($)

Example: to find all possible endings related to the word cardiac, enter root cardi*  to retrieve cardiac, cardiovascular, cardiology, cardiomyopathy, etc

 

Wildcards for Keyword Searching In addition to truncation, wildcards can be used in keyword searches. The wildcard is represented by a question mark ? or a hash tag # placed in the middle of a word to account for possible different spellings of the same word.

Use the ? wildcard to replace an unknown character in your term so that your search returns all alternate spellings for that word. 

 Example: Type analy?e to find all citations containing analyze & analyse.

Add the # wildcard in your search term where an alternate spelling may contain an extra character. This search finds all citations of the word that appear with or without the extra character.

Example:  Enter p#ediatric to find all citations containing pediatric or paediatric.

Search tips for PubMed

PubMed is a free web-based interface for searching MEDLINE

  • PubMed is created by the National Library of Medicine & contains the MEDLINE database 
  • It indexes journal articles in medicine, nursing, dentistry, veterinary medicine & the health care system
  • PubMed provides abstracts of journal articles (currently over 24 million) published in 5,600 journals in 30 languages dating back to 1946
  • It does not include meeting abstracts, conference proceedings, dissertations, patents, or websites
  • NLM indexers add Medical Subject Headings (MeSH) to the information about each article. Searching with MeSH  helps you find relevant articles quickly.

PubMed Basic Quick Search

Basic Search Tips

Finding a few good articles on a specific topic is quick & easy.

You are looking for articles about chemotherapy & colorectal cancer. 

Type your keywords into the search box:  PubMed searches for keywords in the article title, abstract & subject headings. Results are automatically sorted by Best match (i.e. most relevant to your terms). Choose from the other DISPLAY OPTIONS to sort according to your needs.

 pubmed basic search screen

 

Advanced Search Tips

To run a more complex search select Advanced to:

  • use a combination of keywords & MeSH
  • incorporate Boolean operators, truncation & field tags
  • use MeSH terms

 

 

The most valuable 17 minutes you will spend

Search tips for MEDLINE Complete

Ebsco MEDLINE Complete is a user friendly interface for searching  all abstracts from the Medline subset of PubMed. MEDLINE uses MeSH (Medical Subject Headings) to index all articles from its select list of 5200+  biomedical journals. Medline Complete provides direct links to full text Medline content available via UNic.

Search Tips

Basic Search Tips

To create a basic search:

1. Enter your terms in the search bar

2. Click on the Search Options and select a specific search mode such as ''Apply related words'' or apply Limiters such as ''Full Text''

 

3. Click on the Search button and the results display

 

To conduct a search using MeSH:

Follow the steps descibed on the example below to learn how to search in MEDLINE Complete using MeSH

 

Advanced Search Tips

In order to run a well-rounded search through EBSCO MEDLINE, this video will walk you through the steps you need to follow

Proximity searching allows you to search based on how closely two or more search terms appear in the search results.

The proximity operators are composed of a letter (W or N) and a number (to specify the number of words).

Proximity Operators

W# = with

  • With specifies that words appear in the order you type them 
  • Substitute the # with a number of words that may appear in between. If no number is given, then it specifies an exact phrase
Advance search  With(W)

N# = near

  • Near specifies that the words may appear in any order
  • Substitute the # with a number of words that may appear in between
  • MEDLINE will return the search results which contain terms including words in any order.
Advanced search  Near (N)

IMPORTANT! Different databases use different proximity operators. Check the help menu of the database you're searching to find out  what symbols it uses.

 

 

 

 

 

Referencing your research

Grey Literature

Supplement your databse search

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