Ninety residents of a retirement community were selected at random. Each member of the sample was asked a number of questions, including questions about exercise and blood pressure. Residents who exercised more often were less likely to have high blood pressure. Is this an observational study or an experiment?

observational study

Explanation:

An observational study differs from an experimental study, in that researchers only observe the effect of a treatment, risk factor and other factors without altering the subjects. This enables the researcher to draw inferences from the subjects in  a population.

In an experimental study, subjects are randomly assigned to treatment groups and given treatments, results are then analyzed to make inferences.

In the question above, the subjects (residents) were not given any form of treatments, questionnaires were only given to observe the effect of exercise on blood pressure, therefore, it is an observational study.