This part of the book introduced two basic descriptive statistics, the av-

erage and the standard deviation; histograms were used to summarize data. For many data sets, the histogram follows the normal curve. Chapter 6 illustrates these ideas on measurement data. Later in the book, histograms will be used for prob-

ability distributions, and statistical inference will be based on the normal curve.

This is legitimate when the probability histograms follow the curve—the topic of chapter 18. P-698