**Question:** Case control study, All can be measured except - a) Relative risk b) Incidence c) Odds ratio d) Cause & effect relation

**Core Concept:** A case-control study is a type of observational study design in epidemiology that compares the characteristics of cases (those with a disease or condition of interest) with controls (individuals without the disease or condition). The study aims to identify risk factors or causes of the disease or condition under investigation.

**Why the Correct Answer is Right:** Among the given options, only one cannot be measured in a case-control study. Relative risk (RR) is a risk measure that quantifies the strength and direction of the association between an exposure and an outcome, comparing the risk in the exposed group to the risk in the nonexposed group. Incidence refers to the number of new cases occurring within a defined population and time period. Odds ratio (OR) is a measure of the association between an exposure and an outcome, comparing the odds in the exposed group to the odds in the nonexposed group. Lastly, cause-effect relation refers to the relationship between an exposure and an outcome, where exposure directly leads to the outcome. This is a concept distinct from the study design itself, and thus, it cannot be measured in a case-control study.

**Why Each Wrong Option is Incorrect:**

**Option A (Incidence):** Incidence is a measure of the number of new cases occurring within a defined population and time period. Since it is a measure of disease occurrence rather than a study design element, it cannot be considered as one of the things that cannot be measured in a case-control study.

**Option B (Odds Ratio):** Odds ratio is a measure of the association between an exposure and an outcome, comparing the odds in the exposed group to the odds in the nonexposed group. As it is a measure of the association between an exposure and an outcome, it cannot be considered as one of the things that cannot be measured in a case-control study.

**Option C (Odds Ratio):** Odds ratio is a measure of the association between an exposure and an outcome, comparing the odds in the exposed group to the odds in the nonexposed group. As it is a measure of the association between an exposure and an outcome, it cannot be considered as one of the things that cannot be measured in a case-control study.

**Option D (Cause-effect relation):** Cause-effect relation refers to the relationship between an exposure and an outcome, where exposure directly leads to the outcome. This is a concept distinct from the study design itself, and thus, it cannot be measured in a case-control study.

**Core Concept:** A case-control study is a type of observational study design in epidemiology where the cases (individuals with an outcome of interest) are identified first, and then controls (individuals without the outcome of interest) are identified. The study aims to identify risk factors or causes associated with the outcome.

**Why Option E (Cause-effect relation) is Incorrect:** Cause-effect relation refers to the relationship between an exposure and an outcome, where exposure directly leads to the outcome. In a case