19 min. This program begins with an explanation of the difference between a Population and a Sample, and the reasons why samples are so important in estimating data relating to populations too large or too impractical to be measured in their entirety. The program emphasizes the need for random samples, explains how several random samples of the same size will vary, and then looks at ways of dealing with this variability, calculating the Standard Error of the Mean, and how to estimate the "95% Confidence Interval". The program goes on to show how,when,dealing with quantitative data, you can calculate the size of the sample that is needed in order to achieve the precision required.