Question

researchers periodically survey a few thousand of the patients taking a certain medication in order to make connections between that medication and the subjects general health. this method of gathering data is classified as

a census.

a sample survey.

an experiment.

an observational study.

Explanation:

A census involves collecting data from an entire population. Here, only a few thousand patients (a subset of all patients taking the medication) are surveyed, so it's not a census. An experiment involves manipulating variables. Since no manipulation is done here, it's not an experiment. A sample survey is a type of observational study, but the key here is that researchers are just observing the relationship between the medication and general - health without interfering, which is characteristic of an observational study.

Answer:

D. an observational study