The article "Teenage Physical Activity Reduces Risk of Cognitive Impairment in Later Life" (Journal of the American Geriatrics Society [2010]) describes a study of more than 9000 women from Maryland, Minnesota, Oregon, and Pennsylvania. The women were asked about their physical activity as teenagers and at ages 30 and 50. A press release about this study (www.wiley.com) generalized the results of this study to all American women. In the press release, the researcher who conducted the study is quoted as saying Our study shows that women who are regularly physically active at any age have lower risk of cognitive impairment than those who are inactive but that being physically active at teenage is most important in preventing cognitive impairment. Answer the following four questions for this observational study.
a. What is the population of interest?
b. Was the sample selected in a reasonable way?
c. Is the sample likely to be representative of the population of interest? d. Are there any obvious sources of bias?