Case-control

Case-control

1. Backwards directionality

2. Retrospective timing

3. Advantages

   • cheaper and quicker than cohort
   • smaller sample size
   • good far rare diseases chronic diseases and diseases with long latency periods
   • evaluate a variety of different exposures

4. Disadvantages

   • risk of selection bias
   • only study one disease
   • information bias
   • not good for rare exposures
   • risk of disease cannot be estimated directl - due to backwards directionality

5. control group and an exposure group

   • population based controls
     • Advantage = cases and controls come from the same source
     • methods
       • andom telephone dialling
       • friends or heighbourhood
     • disadvantage = hard to enroll subjects & unlisted numbers
   • psital based controls
     • diseases other than exposure
     • dont show good representation of population
     • controls are easily accessable
     • real association of disease to exposure may be missed

6. analysis by actual experience

7. measure of association by ODDS RATIO