in the national AIDS behavioral surveys sample of 2673 adult heterosexual, .2% (thats .0002 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 cant use the large-sample confidence interval to estimate the proportion p in the population who share these two risk factors. Solution Due to personal bias and non response bias, the results so obtained from the sample are more likely to be under estimates. Some respondents may underreport to the question whether they had a sexual partner from a group at high risk of AIDS because of embarrassment and fear or they may forgot or not know the details of their own or partners status of blood transfusion. Since the results are underestimates use of large-sample confidence interval to estimate the population proportion p is not appropriate..