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Medical Literature Searching

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

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 aspects 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.