Harvard Women’s Health Watch reported on a 2016 study on the association between various forms of exercise and health. In this study, researchers used data from large British and Scottish health studies to see if some forms of activity had greater health benefits than others. They examined the association between six different types of exercise with the overall risk of death and death from cardiovascular disease in particular.

Researchers found that racket sports were associated with the greatest reduction in risk of death from any cause, including cardiovascular disease, followed by swimming, aerobics, and cycling. Whatever activity participants chose, risk of death dropped the more often they exercised.

Was this more likely to have been a controlled experiment oran observational study? How do you know?