Question

A stratified sample is sometimes recommended when

• the sample size is very large.

• the population is small compared to the sample.

• distinguishable strata can be identified in the populations.

• the population is spread out geographically.

Answer 1

distinguishable strata can be identified in the populations.

In stratified sampling, the population is divided into different strata and sample are selected from each strata. This is done to make sure that there are representatives of each strata in the sample selected. This can be done when we can divide the sample into several mutually exclusive sub groups, which are called strata. For example, a population can be divided into strata based on their nationality. If we want members from each nationality to be present in the sample, a simple random sample cannot guarantee that. So, we randomly select people from each nationality to form our sample. Here, distinguishable strata (nationality) can be identified in population and a representative sample is taken using this strata.