PS: Case-Control Study Design

Question 1

Name a type of observational study.

Answer 1

Cross-sectional surveys

Question 2

Name 2 types of analytical studies.

Answer 2

1. Cohort studies

2. Case- Control studies

Question 3

Name a type of experimental study.

Answer 3

RCT

Question 4

How do you conduct a case-control study?

Answer 4

1. Identify a group of cases
2. Indentify a suitable group of non-cases (controls)
3. Ascertain previous exposure status of everyone using a study investigator
4. Compare level of exposure in cases and controls

Question 5

How do you calculate odds ratio (OR)?

Answer 5

ad/bc

NOTE: when you lay out the table correctly i.e. cases followed by controls as the columns, exposed followed by unexposed in rows.

Question 6

How do you calculate the 95% CI (confidence intervals)?

Answer 6

Lower CI: Odds ratio / e.f.

Upper CI: Odds ratio x e.f.

Question 7

How many controls should be selected per case?

What affect does this have on the odd ratio?

Answer 7

• Typically up to 4 to 6 times

- The precision of OR is affected by the number of controls

Question 8

Describe some issues with case-control studies

Answer 8

• Selection Bias
• Information bias (Random inaccurate measurements or systematic)
• Confounding factors