EXAMPLE 3.26

A stratified sample of countries. In Examples 3.23 and 3.24, we selected SRSs of size 25 from the population of 189 countries in the World Bank file with data on starting businesses. Let’s think about using a stratified sample. You still want to select 25 companies to examine in detail.

Let’s classify each of the countries as located in Asia, Africa, Europe, North or South America, and Other. We have five strata, and we want a total of 25 countries to examine in detail. Therefore, we need to sample five countries from each stratum. We take an SRS of size 5 from each of these strata.