In epidemiology, the relative frequency of a disease is expressed as the proportion of individuals affected, typically expressedas a percentage, or per thousand individuals. Another important measure is the odds, which represents the ratio of affectedindividuals to unaffected individuals, calculated by dividing by the proportion of affected individuals by the proportion ofunaffected individuals. To assess whether a specific factor increases or decreases the risk of disease, researchers comparethe proportion of affected individuals in an exposed group (where the factor is present) with an unexposed group (wherethe factor is absent). This comparison can be quantified using three key measures: Risk Difference (RD): The absolutedifference in disease risk between the exposed and unexposed groups. Relative Risk (RR): The ratio of disease risk in theexposed group to that in the unexposed group. Odds Ratio (OR): The ratio of the odds of disease in the exposed groupto the odds in the unexposed group. While risk reflects the proportion of individuals affected within a population, oddsrepresent the ratio of affected to unaffected individuals. The OR is particularly useful in case-control studies because it canapproximate the RR when diseases are rare, providing valuable insights even when direct risk calculations are not feasible.