A population consists of N = 10 primary units, each of which consists of Mi = 6 secondary units. A two-stage sampling design selects 2 primary units by simple random sampling (without replacement) and 3 secondary units from each selected primary unit, also by simple random sampling. The observed values of the variable of interest are 7, 5, 3 from the first primary unit selected and 4, 2, 3 from the second primary unit selected.
(a) Estimate the population mean μ per secondary unit.
(b) Estimate the variance of the estimator above.