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 surveying an entire population. Here, only a few thousand patients out of all taking the medication are surveyed, so it's not a census. An experiment involves manipulating variables. Since no manipulation is mentioned, it's not an experiment. A sample survey is a type of observational study. An observational study just observes and records data without intervention, which is what's happening here as researchers are just surveying patients to find connections between the medication and health.

Answer:

D. an observational study