Case Control Studies Flashcards
What is a case control study?
Identifying a group of cases
Identifying a group of non cases (controls)
Ascertaining their level of exposure
Comparing levels of exposure
Advantages of case control over cohort?
Cohort takes longer
Cohort are expensive
Cohort are not good for rare events
How to do analyses case-control studies?
Using odds ratio
AxD/BxC
Use ef and 95% confidence interval
What period of time does case-control look at?
Retrospective
Always looks back in time
Given status now was it the OR of previous exposure
What is conventional case-control?
Looking at retrospective data from recall
What is a nested case-control study?
Collecting data from evolving outcomes and exposure databases
What are the advantages of nested case-control studies?
Over conventional case control; IRR can be calculated
-population already defined
Over conventional cohort; collect more detailed info
What are the main issues of case-control studies?
Selection bias
Information bias
Confounding factors
What is selection bias and how it it dealt with?
Eg, selecting patients from resp ward in relation to smoking
Smoking causes other resp diseases so not repressive of whole
Underestimate OR
Cases should be representative of all cases and controls should be representative all whole population
What is information bias?
Non differentiated misclassification (random inaccurate measurement)
Systemic misclassification
How can be cofounding be adjusted for?
Minimised by matching using cofounders
Adjusted for by analysis of data
