Most cases of cervical cancer are linked to a few strains of the human papilloma

Question

Most cases of cervical cancer are linked to a few strains of the human papilloma virus (HPV). The pharmaceutical company Merck developed a vaccine (Gardasil) against these HPV strains. Worldwide clinical trials followed young women 16 to 26 years of age after vaccination or administration of a placebo for two to four years for signs of HPV-caused cervical cancer. Of 8460 women given Gardasil, none developed HPV-caused cervical cancer. In contrast, 53 of the 8487 women given a placebo did. (a)-why should we not use the large-sample confidence interval for these data? (b) Give the plus four 95% confidence interval for the difference between the two population proportions of women developing HPV-caused cervical cancer.

Explanation / Answer

Ans-

Human papillomaviruses (HPVs) are a group of more than 200 related viruses. More than 40 HPV types can be easily spread through direct sexual contact, from the skin and mucous membranes of infected people to the skin and mucous membranes of their partners. They can be spread by vaginal, anal, and oral sex (1). Other HPV types are responsible for non-genital warts, which are not sexually transmitted.

Sexually transmitted HPV types fall into two categories:

HPV infections are the most common sexually transmitted infections in the United States. About 14 million new genital HPV infections occur each year (4). In fact, the Centers for Disease Control (CDC) estimates that more than 90 percent and 80 percent, respectively, of sexually active men and women will be infected with at least one type of HPV at some point in their lives (5). Around one-half of these infections are with a high-risk HPV type (6).

Most high-risk HPV infections occur without any symptoms, go away within 1 to 2 years, and do not cause cancer. Some HPV infections, however, can persist for many years. Persistent infections with high-risk HPV types can lead to cell changes that, if untreated, may progress to cancer.

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