A psychologist observes the study habits and test scores of high school students to see if those who study more hours tend to achieve higher scores. The students are not given any instructions about how much to study. Is this an observational study or an experiment? Justify your answer.

Experiment, because students were assigned to study different amounts

Observational study, because the psychologist only observed study habits and test scores

Experiment, because the psychologist manipulated the test scores

Observational study, because the psychologist assigned study schedules