Critical appraisal checklist: Case-control study
Gwasanaeth Tystiolaeth
Evidence Service
Questions to assist with the critical appraisal of a case-control study (Type IV
evidence)1
Paper citation:
A. What is this paper about?
Yes
Can’t tell
No
1. Is the study relevant to the needs of the Project?
2. Does the paper address a clearly focused issue? In
terms of:

aims of the investigation?

setting (location and dates)?

the population studied?

case definition explicit and confirmed?

the outcomes considered?
3. Is the choice of study method appropriate to the study
question? ie is the outcome rare or harmful?
1
Sources used: Critical Appraisal Skills Programme (CASP, Anglia and Oxford RHA) questions and Polgar A, Thomas SA. Chapter 22. Critical evaluation of published research in Introduction to
research in the health sciences. 3rd edition. Melbourne: Churchill Livingstone, 1995; Undertaking systematic reviews of research on effectiveness. University of York: NHS Centre for Reviews &
Dissemination, 2001; Weightman AL, Barker, JM, Lancaster J. Health Evidence Bulletins Wales Project Methodology 3. Cardiff: UWCM, 2000.
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Critical appraisal checklist: Case-control study
Is it worth continuing? Yes/No/Discuss
Only complete the next section if the answer to the question above was ‘Yes’
B. Can I trust this paper?
Yes
Can’t tell
No
4. Were the cases recruited in an acceptable way (was
there selection bias)?
 Are the cases defined precisely? Is there anything special
about the cases?

Were the cases representative of a defined population
(geographically or temporally)?

Was there a clear and reliable system for selecting all the
cases?

Are they incident or prevalent?

Is the time-frame of the study relevant to the
disease/exposure?

Did the study have enough participants to minimise the play
of chance – was a power calculation made?
Were the controls randomly selected from the same
population as the cases?

5. Were the cases recruited in an acceptable way (was
there selection bias)?
 Were the controls randomly selected, matched or
population-based? Were they from a defined population?
 Was there anything special about the controls?

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What was the response rate? Could non-respondents be
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Critical appraisal checklist: Case-control study
different in any way?

Was there a sufficient number of controls recruited?
6. Have confounding and bias been considered?

Have all possible explanations of the effects been
considered?

Were sources of data and method of measurement
comparable across groups cases and controls?

Were methods of measurement Objective? Subjective?
Validated?
Yes

Did the study incorporate blinding where appropriate and
feasible?

Did the exposure of interest precede the outcome?

What confounding factors have been considered? Have the
authors missed any potential confounders?

How comparable are the cases and controls with respect to
potential confounding factors (case-control study)?
Can’t tell
No
7. Is the study design and/or execution flawed to the
extent that the results are unreliable?
Is it worth continuing? Yes/No/Discuss.
Only complete the next two sections if the answer to the question above was ‘Yes’
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Critical appraisal checklist: Case-control study
C. What did they find?
Yes
Can’t tell
No
8. Are tables/graphs adequately labelled and
understandable?
9. Are you confident with the authors' choice and use of
statistical methods, if employed?

If sub-group/interactions analyses have been undertaken
is there an explanation of how/why sub-groups have been
formed?

Have all important variables been considered?

Is there an explanation of how potential confounding
factors have been controlled/adjusted for?

Is there an explanation of how missing data/loss to followup have been handled?

Are both unadjusted and adjusted results given?

Is the precision of estimates (95% CI) given?
Yes
Can’t tell
No
10. How strong is the association between exposure
and outcome (look at the odds ratio)? How precise is
this (p-value, CI)?
11. Has adjustment for confounding made any
difference? Might confounding still explain the
association?
12. Do you believe the results?
Can they be due to chance, bias or confounding?
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Do the results meet Bradford-Hill’s criteria: time-sequence,
dose-response, strength, biological plausibility)?
D. Are the results relevant locally?
Yes
Can’t tell
No
13. Can the results be applied to the local situation?
Consider differences between the local and study populations
(eg cultural, geographical, ethical) which could affect the
relevance of the study.
14. Were all important outcomes/results considered?
15. Is any cost-information provided?
16. Accept for further use as Type IV evidence?
If the answer to question 16 above was ‘Yes’ then record this study as ‘Included’ and proceed to data extraction
Comments:
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