The article “Display of Health Risk Behaviors on MySpace by Adolescents” (Archives of Pediatrics and Adolescent Medicine [2009]:27–34) described a study in which researchers looked at a random sample of 500 publicly accessible MySpace web profiles posted by 18-year-olds. The content of each profile was analyzed.

One of the conclusions reported was that displaying sport or hobby involvement was associated with decreased references to risky behavior (sexual references or references to substance abuse or violence).

a. Is the study described an observational study or an experiment?

b. Is it reasonable to generalize the stated conclusion to all 18-year-olds with a publicly accessible MySpace web profile? What aspect of the study supports your answer?

c. Not all MySpace users have a publicly accessible profile. Is it reasonable to generalize the stated conclusion to all 18-year-old MySpace users? Explain.

d. Is it reasonable to generalize the stated conclusion to all MySpace users with a publicly accessible profile?

Explain.