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. | |
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.
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