Case-Control and Cohort Study Questions

In a case-control study, the following data are obtained: Exposure | Cases | Controls | Exposed | 40 (a) | 60 (b) | Unexposed | 10 (c) | 90 (d) | Which statements are CORRECT?

• Odds Ratio = (40×90)/(60×10)

• OR = 6

• Exposure rate among cases = 80%

• Exposure rate among controls = 40%

• Incidence can be calculated

Using the same data in Q1, which interpretations are correct?

• Exposure increases disease risk

• Exposure is protective

• Odds of exposure among cases are higher

• Disease is 6 times more common in exposed

• OR approximates RR only if disease is rare

Which calculations are REQUIRED before Odds Ratio calculation?

• Identify a, b, c, d

• Calculate exposure rate among cases

• Calculate exposure rate among controls

• Calculate incidence

• Create 2×2 table

In a case-control study, OR = 1. What conclusions are valid?

• No association exists

• Exposure neither increases nor decreases odds

• Exposure is harmful

• Odds of exposure are equal in cases and controls

• Incidence is equal

Which conditions MUST be met to interpret OR as RR?

• Disease is rare

• Controls represent non-diseased population

• Follow-up data available

• Cases represent diseased population

• Exposure assigned randomly

A cohort study reports the following: Smoking | Lung Cancer | No Lung Cancer | Total | Yes | 50 (a) | 4950 (b) | 5000 | No | 5 (c) | 4995 (d) | 5000 | Which are CORRECT?

• Incidence among smokers = 10 per 1000

• Incidence among non-smokers = 1 per 1000

• RR = 10

• AR = 9 per 1000

• OR is preferred measure

Which formulas are CORRECT for cohort studies?

• RR = Ie / Iu

• AR = Ie − Iu

• OR = ad/bc

• Incidence = new cases / population at risk

• Prevalence = existing cases / population

If RR = 1.0, which interpretations are valid?

• No association

• Equal risk in exposed and unexposed

• Exposure is protective

• Exposure increases risk

• Incidence is identical

If RR 1

• Exposure has no attributable effect

• Disease due to exposure is zero

Which measures REQUIRE follow-up data?

• Incidence

• Relative Risk

• Attributable Risk

• Odds Ratio

• Morbidity surveillance