Samples, comparisons, and missing cases

We often learn about a large group by examining part of it. A survey asks some residents about a neighborhood. A quality check inspects some items from a production run. A review collects some customers' experiences.

The selected part is a sample. The wider group we want to understand is the population. A sample can be useful without including everyone, but its selection matters as much as its size. This lesson explains when a sample gives a fair picture and when missing cases can distort it.