Written Survey and Computer Survey In a study of 1700 teens aged 15–19, half were given written surveys and half were given surveys using an anonymous computer program. Among those given the written surveys, 7.9% say that they carried a gun within the last 30 days. Among those given the computer surveys, 12.4% say that they carried a gun within the last 30 days (based on data from the Urban Institute).

a. The sample percentages of 7.9% and 12.4% are obviously not equal, but is the difference significant? Explain.

b. Construct a 99% confidence interval estimate of the difference between the two population percentages, and interpret the result.