CAT: CASE-CONTROL STUDIES CASP Flashcards
Did the study address a clearly focused issue?
PICO
Did the authors use an appropriate method to answer their question?
Is a case-control study appropriate for this q?
Did it address the study q?
Were the cases recruited in an acceptable way?
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 e.g. in the practice paper they use recruitment criteria which woild increase the comparability of the study!
Are they incident or prevalent
Is there something special about the cases
Is the time frame of the study relevant to disease/exposure
was there a sufficient number of cases selected
Was there a power calculation
SELECTION BIAS WHICH MAY COMPROMISE VALIDITY
Were the controls selected in an acceptably way?
were the controls representative of the defined population (geographically and/or temporally) i.e. controls and cases must come from the same population
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
SELECTION BIAS WHICH MAY COMPROMISE GENERALISABILITY
Was the exposure accurately measured to minimise 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)
MEASUREMENT, RECALL OR CLASSIFICATION BIAS
Aside from the experimental intervention, were the groups treated equally?
Have the authors taken account of the potential confounding factors in the design or analysis?
Genetic, environment, socio-economics
Look for restriction in design and techniques e.g. modelling, stratified, regression or sensitivity analysis to correct/control/adjust for confounding
Confounding definition -distortion (or potential for distortion) of association between outcome and exposure by a third factor which has an association with both exposure and outcome
Not identifying all important confounders would lead to bias
How large was the treatment effect?
What are the bottom line results
Is the analysis appropriate to the design
How strong is the association between exposure and outcome (look at the odds ratio)
Are the results adjusted for confounding, and might confounding still explain the association
Has adjustment made a big difference to the OR
How precise was the estimate of the treatment effect?
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
Do you believe the results?
big effect is hard to ignore!
Can it be due to chance, bias, or confounding
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 plausibilit
Can the results be applied to the local population?
Are the subjects covered in the study could be sufficiently different from your population to cause concern
Is your local setting is likely to differ much from that of the study
can you quantify the local benefits and harms
From practice paper: what to look for in the main paper
Look for description of the study sample to allow comparison to local population
Consideration of whether the pattern of exposures are likely to be similar to the local population
Information to allow for assessment of internal validity as, if not valid, its not possible to apply results externally
Do the results of the study fit with other evidence?
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.
HINT: Consider all the available evidence from RCT’s Systematic Reviews, Cohort Studies, and Case Control Studies as well, for consistency
Outline how to interpret the odds/odds ratio/95% CI in a case-control study?
Odds in control group will be 1 as its the comparison for the cases!
If the odds ratio for the case group is 0.08 then you say ‘the odds of XYZ are x0.08 of a ZYX. The true value of odds for the risk in the wider population are 95% certain to be between X-Z
