A study published in 2010 showed that city dwellers have a 21% higher risk of developing anxiety disorders and a 39% higher risk of developing mood disorders than those who live in the country. A follow-up study published in 2011 used brain scans of city dwellers and country dwellers as they took a difficult math test. To increase the stress of the participants, those conducting the study tried to humiliate the participants by telling them how poorly they were doing on the test. The brain scans showed very different levels of activity in stress centers of the brain, with the urban dwellers having greater brain activity than rural dwellers in areas that react to stress.

(a) Is the 2010 study an experiment or an observational study?

(b) Can we conclude from the 2010 study that living in a city increases a person’s likelihood of developing an anxiety disorder or mood disorder?

(c) Is the 2011 study an experiment or an observational study?

(d) In the 2011 study, what is the explanatory variable and what is the response variable? Indicate whether each is categorical or quantitative.

(e) Can we conclude from the 2011 study that living in a city increases activity in stress centers of the brain when a person is under stress?