An experiment to determine if an online intervention can reduce references to sex and substance abuse on social networking web sites of adolescents is described in the paper "Reducing At-Risk Adolescents' Display of Risk Behavior on a Social Networking Web Site" (Archives of Pediatrics and Adolescent Medicine [2009]: 35-41). Researchers selected public MySpace profiles of people who described themselves as between 18 and 20 years old and who referenced sex or substance use (alcohol or drugs) in their profiles. The selected subjects were assigned at random to an intervention group or a control group. Those in the intervention group were sent an e-mail from a physician about the risks associated with having a public profile and of referencing sex or substance use in their profile. Three months later, networking sites were revisited to see if any changes had been made. The following excerpt is from the paper: At baseline, 54.2% of subjects referenced sex and 85.3% referenced substance use on their social networking site profiles. The proportion of profiles in which references decreased to 0 was 13.7% in the intervention group vs. 5.3% in the control group for sex (P =.05) and 26% vs. 22% for substance use (P =.61). The proportion of profiles set to "private" at follow-up was 10.5% in the intervention group and 7.4% in the control group (P = .45). The proportion of profiles in which any of these three protective changes were made was 42.1% in the intervention group and 29.5% in the control group (P =.07).

a. The quote from the paper references four hypothesis tests. For each test, indicate what hypotheses you think were tested and whether or not the null hypothesis was rejected.

b. Based on the information provided by the hypothesis tests, what conclusions can be drawn about the effectiveness of the e-mail intervention?