Which population figure served as the denominator when calculating TB incidence and prevalence in this dataset?

Which population figure served as the denominator when calculating TB incidence and prevalence in this dataset?

• A. 264,000
• B. 26,000
• C. 194,000
• D. 183,000

Answer: (D)

The key idea is that rates are made meaningful by using the size of the population being studied as the denominator. For TB, incidence uses the number of new cases divided by the population at risk during the time period, and prevalence uses all existing cases divided by the total population at a specific time. In this dataset, the study area has 183,000 people, so that figure is used as the denominator for both incidence and prevalence calculations. The other numbers in the list are not the population of the study area, so they wouldn’t properly standardize the rates. For context, if there were 150 new TB cases, the incidence rate would be (150 / 183,000) × 100,000, and if there were 300 existing TB cases, the prevalence would be (300 / 183,000) × 100,000.

The key idea is that rates are made meaningful by using the size of the population being studied as the denominator. For TB, incidence uses the number of new cases divided by the population at risk during the time period, and prevalence uses all existing cases divided by the total population at a specific time. In this dataset, the study area has 183,000 people, so that figure is used as the denominator for both incidence and prevalence calculations. The other numbers in the list are not the population of the study area, so they wouldn’t properly standardize the rates. For context, if there were 150 new TB cases, the incidence rate would be (150 / 183,000) × 100,000, and if there were 300 existing TB cases, the prevalence would be (300 / 183,000) × 100,000.