Question

Cross product ratio is determined by which type of study?

• A. Case control
• B. Cohort
• C. Cross sectional
• D. Randomised controlled trial (RCT)

Hint:

Odds ratio = ad/bc, the measure of choice in retrospective designs.

Answer 1

The Correct Option is A

Step 1: The term "cross product ratio" is another name for the odds ratio. It is computed from a 2x2 table as \((a \times d) / (b \times c)\), which is why it is called a cross product.
Step 2: In a case-control study, subjects are selected on the basis of disease status (cases vs controls) and their past exposure is compared. Because incidence cannot be measured directly here, the strength of association is expressed as the odds ratio, i.e. the cross product ratio.
Step 3: Cohort studies measure incidence directly and report relative risk, not the cross product ratio. Cross sectional studies give prevalence, and an RCT estimates risk/relative risk from an experimental design. Hence the correct answer is the case-control study.