Pregnancy, II. The San Diego reproductive clinic in Exercise 24 wants to publish updated information on its success rate.
a) The clinic wants to cut the stated margin of error in half. How many patients' results must be used?
b) Do you have any concerns about this sample? Explain.
Exercise 24
Payments. In a May 2007 Experian/Gallup Personal Credit Index poll of 1008 U.S. adults aged 18 and over, 8% of respondents said they were very uncomfortable with their ability to make their monthly payments on their current debt during the next three months. A more detailed poll surveyed 1288 adults, reporting similar overall results and also noting differences among four age groups: 18-29, 30-49, 50-64, and 65+.
a) Do you expect the 95% confidence interval for the true proportion of all 18- to 29-year-olds who are worried to be wider or narrower than the 95% confidence interval for the true proportion of all U.S. consumers? Explain.
b) Do you expect this second poll's overall margin of error to be larger or smaller than the Experian/Gallup poll's? Explain.