A massive survey of sexual attitudes and behavior in Britain between 1999 and 2001 contacted 16,998 households and interviewed 11,161 respondents aged 16–44 years (one per responding household). The frequency distributions of ages of men and women respondents were the same. The following results were reported on the number of heterosexual partners that individuals had over the previous five-year period (Johnson et al. 2001).

a. What is the standard error of the mean in men? What is it in women?

Assume that the sampling was random.

b. Which is a better descriptor of the variation among men in the number of sexual partners, the standard deviation or the standard error? Why?

c. Which is a better descriptor of uncertainty in the estimated mean number of partners in women, the standard deviation or the standard error? Why?

d. A mysterious result of the study is the discrepancy between the mean number of partners of heterosexual men and women. If each sex obtains its partners from the other sex, then the true mean number of heterosexual partners should be identical. Considering aspects of the study design, suggest an explanation for the discrepancy.

e. Using the 2SE rule of thumb, calculate an approximate 95%

confidence interval for the mean number of heterosexual partners for men.

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Men Women Sample size, nn 46204620 62286228 Mean 3.83.8 2.42.4 Standard deviation 6.76.7 4.64.6