How to Evaluate the Quality of a Clinical Study
Evaluate a clinical study's quality by asking whether the design suits the question, whether bias and confounding were controlled, whether outcomes were measured reliably, whether the analysis fits the plan, and whether the report is complete and honest. Quality is judged against the study's own purpose and design.
Questions that matter
| Domain | Key questions |
|---|---|
| Question and design | Is the question clear? Does the design fit? |
| Participants | Were they selected in a way that avoids bias? Are eligibility criteria clear? |
| Exposure/intervention | Is it defined and measured consistently? |
| Outcomes | Are they valid, reliable and pre-specified? |
| Comparison | Were groups comparable? Was confounding addressed? |
| Follow-up | How many were lost and why? |
| Analysis | Is the method appropriate? Were assumptions checked? |
| Reporting | Are all outcomes reported? Are limitations discussed? |
| Transparency | Registration, protocol, conflicts and funding |
Reporting guidelines as a check
If the paper follows a guideline (CONSORT for trials, STROBE for observational studies, STARD for diagnostic accuracy), check whether items are present. Missing items do not prove poor conduct but limit your ability to judge it.
Illustrative example
Invented for teaching. A trial of a new exercise programme reports no information on how participants were randomised, no blinding of outcome assessors and 35% loss to follow-up in one group. The authors report a large benefit. The student rates the study as high risk of bias and limits her confidence in the benefit.
Common pitfalls
- Equating quality with sample size.
- Using one score to represent quality without examining domains.
- Mixing up the quality of the study with the quality of the reporting.
Key takeaways
- Judge each domain and then form an overall view.
- Use design-specific tools.
- Be explicit about how conclusions depend on quality.
References and further reading
- Higgins JPT, Thomas J, Chandler J, et al., editors. Cochrane Handbook for Systematic Reviews of Interventions. Cochrane. Link
- Schulz KF, Altman DG, Moher D; CONSORT Group. CONSORT 2010 statement: updated guidelines for reporting parallel group randomised trials. BMJ. 2010;340:c332. doi:10.1136/bmj.c332
- von Elm E, Altman DG, Egger M, et al. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. BMJ. 2007;335:806-808. doi:10.1136/bmj.39335.541782.AD
- Critical Appraisal Skills Programme (CASP) checklists. Link
Related reading
This page is general educational information about research methods. It is not medical, legal or regulatory advice; follow your institution's ethics board and your target journal's instructions.