The concept of the former is obvious. So-called stratified samplin gmeans
dividing the parent population into several types
or layers and then sampling randomly from each layer, not
sampling randomly directly from the parent population. The
advantage of thismethod is it narrows the difference between
different types of individuals through classification, which is
conducive to extracting representative samples and reducing
the sample size.Therefore, compared with random sampling,
stratified sampling has relatively remarkable advantages, but
the precondition is how to classify