Which of the following is a correct step in measuring descriptive epi measurements?

• A. Define numerator, then define denominator, then determine if cases are new or existing
• B. Define denominator, then collect blood samples
• C. Randomize participants
• D. Compute odds ratio

Answer: (A)

In descriptive epidemiology, you start by deciding what you are counting (the numerator) and the population to which that count applies (the denominator). Then you determine whether the cases are new or existing to decide if you’re measuring incidence (new cases over time) or prevalence (all existing cases at a point or period). This order matters because incidence requires identifying new cases and relating them to the at-risk population, while prevalence relates to all current cases within the population. Defining the numerator first clarifies exactly what is being counted, and defining the denominator afterward anchors that count to the appropriate population size.

The other options don’t fit descriptive measurement steps. Collecting blood samples is data collection but not a universal step for describing population rates or proportions. Randomizing participants is an experimental or analytic design maneuver, not a descriptive calculation step. Computing an odds ratio is an analytic measure of association, not a basic descriptive metric like incidence or prevalence.