In this lesson by Gary Kader, Christine Franklin, Tim Jacobbe, and Kaycie Maddox, each student tries two methods for selecting a sample from the population of words in the Gettysburg Address: self-selection and simple random sampling. Then, as a class, students construct dotplots and calculate numerical summaries to show how sample means vary from sample to sample.
Using these plots and numerical summaries, students see self-selected samples tend to over-represent the longer words in the Gettysburg Address and produce sample means that are larger than the actual population mean (biased sampling method). On the other hand, simple random samples tend to be representative of the population and produce sample means balanced on both sides of the population mean (unbiased sampling method).
Finally, students explore the relationship between sample size and sample-to-sample variability. Students discover that larger random samples produce sample means with less variability.