The following data were obtained in a study in which 1000 nurses were followed for 20 years to examine the hypothesis that use of a certain diet pill is a risk factor for heart attack. Diet Pill Use Heart Attack Yes No Total Yes 30 11 41 No 959 470 500 489 Total 500 1000 . Estimate the number of woman-years contributed by the unexposed group. What information would you need in order to obtain a better estimate of the number of women-years? b. . What is the 20-year risk of heart attack among those who used diet pills? d. What is the prevalence of diet pill use among those who did not have a heart attack? . Do the data suggest that diet pill use is a risk factor for heart attack? Explain.