Case-Control Studies and Odds ratio

Question 1

What is a case-control study?

Answer 1

• Observational study

- Subjects are sampled based upon presence of absence of disease and then their prior exposure status is determined

Question 2

What is an odds ratio?

Answer 2

• A measure of association between the exposure and disease that can be calculated in case-control studies

Question 3

What is matched sampling? What is it supposed to reduce?

Answer 3

• The process of matching cases and controls in an attempt to make these groups more similar to each other with respect to important risk factors.
• Done to control confounding

Question 4

What is confounding?

Answer 4

• Distortion of results that occurs when the apparent effects of the exposure of interest are attributable entirely or in part to the effects of an extraenous variable (a confounder)

Question 5

How do you calculate odds ratio?

Answer 5

Odds ratio = Odds of case exposure / Odds of control exposure
Odds of case exposure = (exposed cases/all cases) / (unexposed cases/all cases)
Odds of control exposure = controls exposed / controls unexposed

** Re-arranged **
= (Cases exposed x controls unexposed) / (Cases unexposed c controls exposed)

Question 6

What are concordant pairs?

Answer 6

• In a matched design a concordant pair is one in which the case and control that are matched have the same exposure status (ie. both exposed or both unexposed)

Question 7

What are discordant pairs?

Answer 7

• In a matched design a discordant pair is on in which the case and control that are matched have a different exposure status (ie. One exposed and the other not)