Ans. a (ad/bc) (Ref: Park, PSM, 22nd/p 70)Screening test resultsDiagnosis diseasedNot diseasedTotalPositivea (true positive)b (false positive)a + bNegativec (False negative)d (True negative)C+dTotala+bb+da+b+c+dODDS RATIO (CROSS-PRODUCT RATIO)# Odds ratio = ad/bc# The odds ratio is a measure of effect size particularly important in Bayesian statistics and logistic regression.# It is defined as the ratio of the odds of an event occurring in one group to the odds of it occurring in another group, or to a data-based estimate of that ratio. These groups might be men and women, an experimental group and a control group, or any other dichotomous classification.# An odds ratio of 1 indicates that the condition or event under study is equally likely in both groups. An odds ratio greater than 1 indicates that the condition or event is more likely in the first group. And an odds ratio <1 indicates that the condition or event is less likely in the first group. The odds ratio must be zero or greater than zero. As the odds of the first group approaches zero, the odds ratio approaches zero. As the odds of the second group approaches zero, the odds ratio approaches positive infinity.RELATIVE RISKRR =Incidence of disease (or death) among exposed-----------------------------Incidence of disease (or death) among non-exposedATTRIBUTABLE RISK=Incidence of disease rate among exposed - Incidence of disease rate among non-exposed--------------------------------------------------Incidence rate among exposedx 100