The Centers for Disease Control (www.cdc.gov) periodically takes large randomized surveys to track health of Americans. In a survey of 11,207 adults in 1976–1980, 47% were overweight (body mass index BMI Ú 25). In a survey of 4431 adults in 2003–2004, 66% were overweight.
a. Estimate the change in the population proportion who are overweight, and interpret.
b. The standard error for estimating this difference equals 0.009. What is the main factor that causes se to be so small?
c. The 95% confidence interval comparing the population proportions is (0.17, 0.21). Interpret, taking into account whether or not 0 is in this interval.