Which measure compares one part of data to another part?

• A. Ratio
• B. Rates/Proportion
• C. Relative risk ratios
• D. Infectivity

Answer: (A)

A ratio is a way to express how much of one part of data there is relative to another part. It simply divides one quantity by another, making it easy to compare two subgroups or conditions within the data—for example, the number of cases in one group versus another. This contrasts with rates, which add a time component (like cases per person-year), and proportions, which relate a part to the whole. Infectivity is a property of a pathogen, not a measure comparing parts of data. Relative risk is itself a specific type of ratio used to compare incidence between groups, but the general concept described by “one part of data to another part” is best captured by the broad idea of a ratio.