Outline four ways of evaluating the strength of association in a cohort study?

1. Relative Risk (RR): Relative risk is a commonly used measure of association in cohort studies. It compares the risk of developing a particular outcome in the exposed group to the risk in the unexposed group. A relative risk greater than 1 indicates a positive association, while a relative risk less than 1 indicates a negative association.

2. Hazard Ratio (HR): Hazard ratio is another measure of association commonly used in cohort studies, particularly in survival analysis. It compares the hazard rate (rate of occurrence of the outcome) in the exposed group to the hazard rate in the unexposed group. A hazard ratio greater than 1 indicates a positive association, while a hazard ratio less than 1 indicates a negative association.

3. Odds Ratio (OR): Odds ratio is often used as a measure of association in case-control studies, but it can also be used in cohort studies. It compares the odds of developing the outcome in the exposed group to the odds in the unexposed group. An odds ratio greater than 1 indicates a positive association, while an odds ratio less than 1 indicates a negative association.

4. Confidence Intervals (CI): Confidence intervals provide a range of values within which the true measure of association is likely to fall. A narrower confidence interval indicates a more precise estimate of the association, while a wider confidence interval indicates greater uncertainty. If the confidence interval includes the null value (e.g., 1 for relative risk or odds ratio), it suggests that the association is not statistically significant.