Suppose a sample of size n is drawn from a population with mean μ and variance σ2. The standard error of the sample mean x̄ is:

Consider a finite population of size N = 100. Let T1 be the sample mean of a study variable based on a sample of size n (1 < n < N) under simple random sampling with replacement (SRSWR). Let T2 be the sample mean under simple random sampling without replacement (SRSWOR). If Var(T1) = 9 Var(T2), then the sample size n equals:

Stratified sampling is most effective when certain variance criteria are fulfilled. Which of the following conditions is INCORRECT regarding optimal stratification?