Chapter 8 Confidence Intervals 8 3 Confidence Intervals

Chapter 8 Confidence Intervals 8. 3 Confidence Intervals about a Population Proportion

EXAMPLE Computing a Point Estimate In a Fox News Poll conducted January 2728, 1999, 911 registered voters nationwide were asked “Have you ever cheated on a person you were in a relationship with? ” Of the 911 respondents, 191 said “yes”. Obtain a point estimate for the proportion of registered voters that have cheated on a person they were in a relationship with.

EXAMPLE Constructing a Confidence Interval for a Population Proportion In a Fox News Poll conducted January 27 -28, 1999, 911 registered voters nationwide were asked “Have you ever cheated on a person you were in a relationship with? ” Of the 911 respondents, 191 said “yes”. Compute a 95% confidence interval for the proportion of registered voters that have cheated on a person they were in a relationship with.

Sample Size Needed for a Specified Margin of Error and Level of Confidence

EXAMPLE Determining Sample Size A sociologist wanted to determine the percentage of residents of America that only speak English at home. What size sample should be obtained if she wishes the estimate to be within 3 percentage points with 90% confidence assuming (a) she uses the 2000 estimate obtained from the Census 2000 Supplementary Survey of 82. 4%. (b) she does not use any prior estimates.