How-to · Step-by-step
Critical appraisal
Critical appraisal is the systematic process of judging a research study’s trustworthiness, value and relevance, weighing its methods and results before relying on its findings.
The step most authors miss
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Step by step
How to do it
1.Check that the study addresses a clear question
Identify the study’s aim, population, intervention or exposure, comparison and outcomes. A focused, well-defined question is the foundation; a vague aim makes the rest of the appraisal difficult and signals a weak study.
2.Assess the validity of the methods
Judge whether the design suits the question and whether it was conducted to minimise bias — for a trial, look at randomisation, allocation concealment, blinding and follow-up. Internal validity is the question of whether the results can be believed.
3.Examine the results
Look at what the study found, the size of any effect, and how precisely it was estimated — for example through confidence intervals. Consider whether the analysis was appropriate and whether the conclusions follow from the data presented.
4.Judge relevance and applicability
Ask whether the study’s population, setting and outcomes match your own question — its external validity. A methodologically strong study may still be of limited use if it was conducted in a very different context from yours.
5.Use a structured appraisal tool
Apply a checklist suited to the study design, such as the CASP checklists for trials, cohort studies, qualitative research and systematic reviews. A structured tool makes appraisal consistent, transparent and harder to skew.
6.Rate the certainty of the wider evidence
When appraising a body of evidence rather than one study, an approach such as GRADE rates the overall certainty — high to very low — considering risk of bias, consistency, directness, precision and publication bias across studies.
Why appraise rather than accept
Not all published research is equally reliable, so a literature review must weigh the evidence rather than treat every study as authoritative. Critical appraisal is the disciplined way of doing this: a structured judgement of how far a study’s design and conduct support its conclusions and how relevant those conclusions are to your own question. It protects a review from being swayed by a large but flawed study, and it lets you give appropriate weight to the strongest evidence. Three questions organise the task — is the study valid, what are its results, and are they relevant to me?
Common questions
FAQ
What is the CASP checklist?+
CASP — the Critical Appraisal Skills Programme — provides free checklists for appraising different study designs, including randomised trials, cohort and case-control studies, qualitative research, diagnostic studies and systematic reviews. Each poses a series of questions about validity, results and relevance, giving reviewers a consistent, structured way to judge a study’s trustworthiness rather than relying on impression alone.
What is the difference between CASP and GRADE?+
CASP checklists appraise individual studies, helping you decide how much to trust one paper. GRADE works at a different level: it rates the overall certainty of a body of evidence for a particular outcome — high, moderate, low or very low — by considering risk of bias, consistency, directness, precision and publication bias across the included studies. The two are complementary, not alternatives.
Do I need to appraise qualitative research differently?+
Yes. Concepts such as randomisation and confidence intervals do not apply to qualitative work, which is appraised for trustworthiness instead — its credibility, dependability, confirmability and transferability, and the rigour of its sampling, data collection and analysis. Tools such as the CASP qualitative checklist are designed for this, so use a tool matched to the study’s design.
