What type of study is it when a researcher tracks 50 puppies without thyroid problems to observe any dietary effects over time?

A prospective study involves following subjects over a period to observe outcomes as they occur. In this scenario, the researcher tracks 50 puppies without thyroid problems, observing how their diet may impact their health over time. This means that the researcher collects data moving forward from the starting point of the study, monitoring various dietary factors and their effects on the puppies' thyroid health.

This approach is beneficial because it allows the researcher to collect data on the dietary habits and any resultant health changes directly, creating a clear link between what the puppies are consuming and any observable health outcomes. This forward-looking method distinguishes it from other study types, such as retrospective studies, which look back at existing data, or cross-sectional studies, which examine a population at a single point in time.