The measure of strength of association between risk factor and outcome is:
**Core Concept**
The core concept here is the measurement of association between a risk factor and an outcome in epidemiological studies. This involves assessing the strength of the relationship between the risk factor and the outcome, often expressed as a ratio or proportion.
**Why the Correct Answer is Right**
The odds ratio (OR) is a measure of association that represents the ratio of the odds of an outcome occurring in the presence of a risk factor to the odds of the outcome occurring in the absence of the risk factor. It is commonly used in case-control studies to quantify the strength of association between a risk factor and an outcome. The odds ratio can be calculated using the following formula: OR = (a/c) / (b/d), where a is the number of cases with the risk factor, c is the number of controls with the risk factor, b is the number of cases without the risk factor, and d is the number of controls without the risk factor. The odds ratio provides a direct measure of the strength and direction of the association between the risk factor and the outcome.
**Why Each Wrong Option is Incorrect**
**Option B:** Attributable risk is a measure of the proportion of cases that can be attributed to a particular risk factor, but it does not provide a direct measure of the strength of association between the risk factor and the outcome.
**Option C:** Relative risk is a measure of the ratio of the probability of an outcome occurring in the presence of a risk factor to the probability of the outcome occurring in the absence of the risk factor. However, it is not as commonly used as the odds ratio in case-control studies.
**Option D:** Poisson's ratio is a measure of the ratio of the stress and strain in materials, and is not relevant to epidemiological studies.
**Clinical Pearl / High-Yield Fact**
When interpreting the odds ratio, it's essential to consider the confidence interval, as a statistically significant odds ratio may not necessarily translate to a clinically significant association.
**✓ Correct Answer: A. Odds ratio**