A 2007 study of women in Miami (Brewer et al., Ann Epidemiol. 17:533-539) examined the link between HIV status and high-risk sexual activity. Eligible participants were female, at least 18 years of age, English-speaking, self-reported having vaginal or anal sex in the past 30 days, and self-reported having smoked crack or snorted or injected cocaine or heroin in the last 30 days and having not been in drug treatment in the last 30 days. The data set HIVrisk.dta (table below) contains two columns: risk for unprotected sex and HIV for HIV status. Each woman knew her HIV status.

Risk for unprotected sex

HIV Yes No Total

Positive 88 29 117

Negative 34 27 61

Total 122 56 178

A) What proportion of the HIV-positive group engaged in unprotected sex? Provide a 95% CI for the true proportion.

Pick one answer: (1.249, 4.647) OR (.672, 0.829)

Please give a step by step explanation as to why the answer is the answer. Thanks.

B) What proportion of the HIV-negative group engaged in unprotected sex? Provide a 95% CI for the true proportion.

Please give a step by step explanation as to why the answer is the answer. Thanks.

C) Test the null hypothesis that the proportion of HIV-positive women having unprotected sex is equal to the proportion of HIV-negative women having unprotected sex (group proportion comparison). Provide the p-value and state the conclusion. Please use statistical software (R commander or R for this question).

**If you use statistical software like R for the questions above, please show your work. Also, please don't copy and paste from other sources. I really want to learn. Thanks.**