Chapter 14, Problem 47E

Exercises 45 through 48 refer to a study on the effectiveness of an HPV (human papilloma virus) vaccine conducted between October 1998 and November 1999. HPV is the most common sexually transmitted infection—more than 20 million Americans are infected with HPV—but most HPV infections are benign, and in most cases infected individuals are not even aware they are infected. (On the other hand, some HPV infections can lead to cervical cancer in women.) The researchers recruited 2392 women from 16 different centers across the United States to participate in the study through advertisements on college campuses and in the surrounding communities. To be eligible to participate in the study, the subjects had to meet the following criteria: (1) be a female between 16 and 23 years of age, (2) not be pregnant, (3) have no prior abnormal Pap smears, and (4) report to have had sexual relations with no more than five men. At each center, half of the participants were randomly selected to receive the HPV vaccine, and the other half received a placebo injection. After 17.4 months, the incidence of HPV infection was 3.8 per 100 woman-years at risk in the placebo group and 0 per 100 woman-years at risk in the vaccine group. In addition, all nine cases of HPV-related cervical precancerous growths occurred among the placebo recipients. [Source: New England Journal of Medicine, 347, no. 21 (November 21, 2002): 1645–1651.]

a. Describe the treatment group in the study.

b. Could this study be considered a double-blind, randomized controlled placebo study? Explain.