CASP Checklist:
11 questions to help you make sense of a Case Control Study
How to use this appraisal tool: Three broad issues need to be considered when appraising a
case control study:
Are the results of the study valid? (Section A)
What are the results? (Section B)
Will the results help locally? (Section C)
The 11 questions on the following pages are designed to help you think about these issues
systematically. The first three questions are screening questions and can be answered
quickly. If the answer to both is “yes”, it is worth proceeding with the remaining questions.
There is some degree of overlap between the questions, you are asked to record a “yes”,
“no” or “can’t tell” to most of the questions. A number of italicised prompts are given after
each question. These are designed to remind you why the question is important. Record your
reasons for your answers in the spaces provided.
About: These checklists were designed to be used as educational pedagogic tools, as part of a
workshop setting, therefore we do not suggest a scoring system. The core CASP checklists
(randomised controlled trial & systematic review) were based on JAMA 'Users’ guides to the
medical literature 1994 (adapted from Guyatt GH, Sackett DL, and Cook DJ), and piloted with
health care practitioners.
For each new checklist, a group of experts were assembled to develop and pilot the checklist
and the workshop format with which it would be used. Over the years overall adjustments
have been made to the format, but a recent survey of checklist users reiterated that the basic
format continues to be useful and appropriate.
Referencing: we recommend using the Harvard style citation, i.e.: Critical Appraisal Skills
Programme (2018). CASP (insert name of checklist i.e. Case Control Study) Checklist. [online]
Available at: URL. Accessed: Date Accessed.
©CASP this work is licensed under the Creative Commons Attribution Non-Commercial-
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Critical Appraisal Skills Programme (CASP) part of Oxford Centre for Triple Value Healthcare Ltd
Section A: Are the results of the trial valid?
1. Did the study address a
clearly focused issue?
HINT: An issue can be focused In terms of
the population studied
Whether the study tried to detect a
beneficial or harmful effect
the risk factors studied
Can’t Tell
2. Did the authors use an
appropriate method to
answer their question?
HINT: Consider
Is a case control study an appropriate
way of answering the question under
the circumstances
Did it address the study question
Can’t Tell
Paper for appraisal and reference:
Is it worth continuing?
3. Were the cases recruited in
an acceptable way?
HINT: We are looking for selection bias
which might compromise validity of the
are the cases defined precisely
were the cases representative of a
defined population (geographically
and/or temporally)
was there an established reliable
system for selecting all the cases
are they incident or prevalent
is there something special about the
is the time frame of the study
relevant to disease/exposure
was there a sufficient number of
cases selected
was there a power calculation
Can’t Tell
4. Were the controls selected in
an acceptable way?
HINT: We are looking for selection bias
which might compromise the
generalisability of the findings
were the controls representative of the
defined population (geographically
and/or temporally)
was there something special about
the controls
was the non-response high, could
non-respondents be different in
any way
are they matched, population
based or randomly selected
was there a sufficient number of
controls selected
Can’t Tell
5. Was the exposure accurately
measured to minimise bias?
HINT: We are looking for measurement,
recall or classification bias
was the exposure clearly defined and
accurately measured
did the authors use subjective or
objective measurements
do the measures truly reflect what
they are supposed to measure (have
they been validated)
were the measurement methods
similar in the cases and controls
did the study incorporate blinding
where feasible
is the temporal relation correct
(does the exposure of interest
precede the outcome)
Can’t Tell
6. (a) Aside from the
experimental intervention,
were the groups treated
HINT: List the ones you think might be
important, that the author may have
6. (b) Have the authors taken
account of the potential
confounding factors in the
design and/or in their
HINT: Look for
restriction in design, and techniques e.g.
modelling, stratified-, regression-, or
sensitivity analysis to correct, control or
adjust for confounding factors
Can’t Tell
Section B: What are the results?
7. How large was the treatment effect?
HINT: Consider
what are the bottom line
is the analysis appropriate to
the design
how strong is the association
between exposure and
outcome (look at the odds
are the results adjusted for
confounding, and might
confounding still explain the
has adjustment made a big
difference to the OR
8. How precise was the estimate of the treatment
HINT: Consider
size of the p-value
size of the confidence intervals
have the authors considered all the
important variables
how was the effect of subjects
refusing to participate evaluated
9. Do you believe the results?
HINT: Consider
big effect is hard to ignore!
Can it be due to chance, bias, or
are the design and methods of this
study sufficiently flawed to make the
results unreliable
consider Bradford Hills criteria (e.g. time
sequence, does-response gradient,
strength, biological plausibility)
Section C: Will the results help locally?
10. Can the results be applied
to the local population?
HINT: Consider whether
the subjects covered in the study could
be sufficiently different from your
population to cause concern
your local setting is likely to differ
much from that of the study
can you quantify the local benefits and
Can’t Tell
11. Do the results of this study
fit with other available
HINT: Consider
all the available evidence from RCT’s
Systematic Reviews, Cohort Studies,
and Case Control Studies as well, for
Can’t Tell
Remember One observational study rarely provides sufficiently robust evidence to recommend changes to
clinical practice or within health policy decision making. However, for certain questions observational
studies provide the only evidence. Recommendations from observational studies are always stronger
when supported by other evidence.
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