A researcher is studying the effects of playing chess on memory improvement. He identifies 50 people who play chess and 50 people who do not. Each of the 100 people is given a questionnaire designed to determine memory level. None of the 100 people who participated in the study knew they were part of a study. Which statement is true? (5 points)

This is a randomized comparative experiment.

This is a double-blind study.

This is a matched-pairs design.

This is an observational study.