In veterinary epidemiology, which statement correctly defines source population, target population, and study population?

• A. Source pop = original population of interest; target pop = the population to which source pop comes from; study pop = the population actually selected to be in the study from source pop.
• B. Source pop = the population to which results are generalized; target pop = original population of interest; study pop = entire population.
• C. Source pop = original population of interest; target pop = where source pop comes from; study pop = the population actually selected to be in the study from source pop.
• D. Source pop = population defined by the researcher’s expectations; target pop = the same as study pop; study pop = individuals who consent.

Answer: (C)

The main idea is to understand how the groups in a study relate to each other in terms of who you’re studying and to whom you want to apply the findings. The source population is the original population of interest from which you could draw your study subjects. The target population is the broader population from which that source population comes—the group you ultimately want to generalize the results to. The study population is the actual set of individuals who are enrolled and observed in the study, drawn from the source population. The statement that best fits this flow says the source is the original population of interest, the target is the larger population from which the source is drawn, and the study population is the subset from the source actually included in the study. This correctly captures the hierarchical sampling path and the distinction between where results are intended to apply and where the data come from. Other options either misstate the generalization target or tie the study population to factors like consent, which aren’t the defining relationships here.