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Systematic Reviews for Health Sciences and Medicine

An introduction to Systematic Reviews, with examples from Health Sciences and Medicine

Overview of Systematic Reviews

A systematic review has a number of features distinguishing it from merely searching systematically.

It is:

  • comprehensive
  • objective
  • transparent
  • fully documented and reproducible
  • conducted across a range of resources

It aims to identify as many relevant studies as possible, even if some will be later excluded on technical grounds. 

It is also

  • time-consuming (it may take 8 hours or more),
  • rigorous and exacting (it maps to subject headings and synonyms to be as comprehensive as possible)
  • and it rates wide recall over specificity (it is sensitive to borderline studies, which may need closer examination in terms of inclusion and exclusion criteria).

The inclusion and exclusion criteria may be based on participant recruitment and follow-up, randomisation, sampling or other details of methodology, and validity. In critical appraisal the significance and generalizability of findings are also assessed.

You might not need a systematic review. It's a scholarly research project usually undertaken by experts. 

If you need an authoritative source summarising the evidence available, a Cochrane review or clinical guidelines may be more appropriate - or perhaps you could conduct a rapid review.

If you're unsure of the extent of the literature, or still finalising the inclusion and exclusion criteria, a scoping review is indicated.

Systematic Reviews: Overview of the Search Process

The Question

Step 1 : Develop a Research Question and Review Approach

Does the question need answers, a decision or the best estimate?

If it needs to be fast and authoritative, conduct a rapid review from the best resources.

Scoping reviews – or a systematic review – take more time and aim to cover more or all available resources.

What will be an acceptable answer?

Is <this> intervention with <these> patients more likely to give <these> outputs than another intervention?

The Strategy

Step 2 : Identify Resources and Build a Search Strategy

Use resources selected for coverage and reputation.

Every question has angles and contexts.

Search with a distinct set of words - concepts - targeting each of the main facets of the question.

Adapt the strategy for searching in each resource.

Record when, where and how you searched and the results.

Save, identify and deduplicate the results for critical appraisal.

The Results

Step 3 : Analyse and Report the Results

The search strategy will not have filtered out all irrelevant results. Refine  the strategy.  Apply exclusion criteria.

Screen out inappropriate studies using exclusion criteria, recording what is  excluded and why.

A review matrix and summary tables can help with compiling results.

A forest plot can visualise statistical results.