In the article "Coffee, Caffeine, and Risk of Depression Among Women" in the September 2011 edition of theArchives of Internal Medicine, researchers investigated the relationship between caffeine consumption and depression among women.

The participants in this study were older, with substantially lower rates of depression when compared to female teens. Researchers compared two groups of women (among others) in this study: those who do not drink coffee and those who routinely drink 4 or more cups of coffee each day.

For the following question, acoffee drinkeris a woman who drinks four or more cups each day.

Which best describes the type of study?

• an experiment comparing two treatments
• an observational study comparing two population