In the National AIDS Behavioral Surveys sample of 2987 adult heterosexuals, 0.4%
ID: 3393591 • Letter: I
Question
In the National AIDS Behavioral Surveys sample of 2987 adult heterosexuals, 0.4% (that's 0.002 as a decimal fraction) had both received a blood transfusion and had a sexual partner from a group at high risk of AIDS. Explain why we can't use the large-sample confidence interval to estimate the proportion p in the population who share these two risk factors.
A. There were not enough "successes". B. The survey studied the proportion of two risk factors, while the large-sample confidence interval is used for a single proportion out of a population. C. There should be no problem using the large-sample confidence interval since the sample size was large. D. Large-sample confidence intervals can never be used when the sample proportion is as small as 0.004.Explanation / Answer
There are not enough successes.
The number of success= np = 0.004*2987= 11.98~12
We don't have at least 15 successes in the sample.