The president of DePaul University wants to conduct a survey to determine the community’s opinion regarding campus safety. The president divides the DePaul community into three groups: resident students, nonresident (commuting) students, and staff (including faculty) so that he can obtain a stratified sample. Suppose there are 6204 resident students, 13,304 nonresident students, and 2401 staff, for a total of 21,909 individuals in the population. The president wants to obtain a sample of size 100, with the number of individuals selected from each stratum weighted by the population size.

So resident students make up 6204/21,909 = 28% of the sample, nonresident students account for 61% of the sample, and staff constitute 11% of the sample. A sample of size 100 requires a stratified sample of 0.28(100) = 28 resident students, 0.61(100) = 61 nonresident students, and 0.11(100) = 11 staff.

Approach To obtain the stratified sample, conduct a simple random sample within each group. That is, obtain a simple random sample of 28 resident students (from the 6204 resident students), a simple random sample of 61 nonresident students, and a simple random sample of 11 staff. Be sure to use a different seed for each stratum.