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©Critical Appraisal Skills Programme (CASP) Cohort Study Checklist 31.05.13

12 questions to help you make sense of cohort study

How to use this appraisal tool

Three broad issues need to be considered when appraising a cohort study:

 Are the results of the study valid? (Section A)

 What are the results? (Section B)

 Will the results help locally? (Section C)

The 12 questions on the following pages are designed to help you think about these issues systematically.

The first two 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.

These checklists were designed to be used as educational tools as part of a workshop setting

There will not be time in the small groups to answer them all in detail!

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©Critical Appraisal Skills Programme (CASP) Cohort Study Checklist 31.05.13

(A) Are the results of the study valid?

Screening Questions

1. Did the study address a clearly focused issue? Yes Can’t tell No

HINT: A question can be ‘focused’ In terms of

 The population studied

 The risk factors studied

 The outcomes considered

 Is it clear whether the study tried to detect a beneficial

or harmful effect?

2. Was the cohort recruited in an acceptable way? Yes Can’t tell No

HINT: Look for selection bias which might compromise

the generalisibility of the findings:

 Was the cohort representative of a defined population?

 Was there something special about the cohort?

 Was everybody included who should have been included?

Is it worth continuing?

©Critical Appraisal Skills Programme (CASP) Cohort Study Checklist 31.05.13

Detailed questions

3. Was the exposure accurately measured to Yes Can’t tell  No

minimise bias?

HINT: Look for measurement or classification bias:

 Did they use subjective or objective measurements?

 Do the measurements truly reflect what you want them

to (have they been validated)?

 Were all the subjects classified into exposure groups

using the same procedure

4. Was the outcome accurately measured to Yes Can’t tell No

minimise bias?

HINT: Look for measurement or classification bias:

 Did they use subjective or objective measurements?

 Do the measures truly reflect what you want them to

(have they been validated)?

 Has a reliable system been established for

detecting all the cases (for measuring disease

occurrence)?

 Were the measurement methods similar in the

different groups?

 Were the subjects and/or the outcome assessor

blinded to exposure (does this matter)?

©Critical Appraisal Skills Programme (CASP) Cohort Study Checklist 31.05.13

5. (a) Have the authors identified all important Yes Can’t tell No

confounding factors?

List the ones you think might be

important, that the author missed.

(b) Have they taken account of the Yes Can’t tell No

confounding factors in the design

and/or analysis? List:

HINT: Look for restriction in design, and techniques e.g.

modelling, stratified-, regression-, or sensitivity analysis

to correct, control or adjust for confounding factors

6. (a) Was the follow up of subjects complete Yes Can’t tell No

enough?

(b) Was the follow up of subjects long Yes Can’t tell No

enough?

HINT: Consider

 The good or bad effects should have had long enough

to reveal themselves

 The persons that are lost to follow-up may have

different outcomes than those available for assessment

 In an open or dynamic cohort, was there anything special

about the outcome of the people leaving, or the

exposure of the people entering the cohort?

(B) What are the results?

7. What are the results of this study?

HINT: Consider

 What are the bottom line results?

 Have they reported the rate or the proportion between

the exposed/unexposed, the ratio/the rate difference?

 How strong is the association between exposure and

outcome (RR,)?

 What is the absolute risk reduction (ARR)?

8. How precise are the results?

HINT: Look for the range of the confidence intervals, if given.

9. Do you believe the results? Yes Can’t tell No

HINT: Consider

 Big effect is hard to ignore!

 Can it be due to bias, chance or confounding?

 Are the design and methods of this study sufficiently

flawed to make the results unreliable?

 Bradford Hills criteria (e.g. time sequence, dose-response

gradient, biological plausibility, consistency)

10. Can the results be applied to the local population? Yes Can’t tell No

HINT: Consider whether

 A cohort study was the appropriate method to answer this question

 The subjects covered in this study could be sufficiently different from

your population to cause concern

 Your local setting is likely to differ much from that of the study

 You can quantify the local benefits and harms

11. Do the results of this study fit with other Yes Can’t tell No

available evidence?

12. What are the implications of this study for practice?

HINT: Consider

 One observational study rarely provides sufficiently robust

evidence to recommend changes to clinical practice or

within health policy decision making

 For certain questions observational studies provide the only

evidence

 Recommendations from observational studies are always stronger

when supported by other evidence