Weekly turnover in a city with... |
• 20 chain grocery stores (high spread) |
Use this diagram to show that disproportionately large samples should be selected from strata with greater variability.
Both halves of the diagram select stratified samples.
Click Take sample to take both kinds of stratified sample. If the sample sizes are disproportionate, the sample mean should be replaced with:
With k strata of size N1, N2, ..., Nk, and samples of size n1, n2, ..., nk, use
Take several more samples and observe that the estimated mean is less variable when more observations are taken from the stratum with more variability.