The mite Demodex folliculorum lives in the hair follicles of humans, including the follicles of the eyelashes. (The bluish creatures in the photo on the first page of this chapter are these mites. The yellowish shaft in the photo is a human hair.) Having heard that “most people” have these mites living in their skin and eyelashes, we wanted to know what “most” really meant. The only data we could find was in a paper that compared 16 North American women with a skin condition called rosacea to 16 women that did not have this skin condition (call this the “control” group). Of the 16 women in the control group, 15 of the 16 had these mites. All 16 of the women in the rosacea group had mites (Al Am et al. 1997).

a. From these data, a researcher estimated the proportion of people in North America who have these mites as  What is wrong with this estimate?

b. What is your best estimate for the proportion of North Americans without rosacea who have these mites? Assume random sampling.

c. What is the 95% confidence interval for this estimate?

d. What is the best estimate (with a 95% confidence interval) for the proportion of women with rosacea who have these mites?

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