Percentiles provide detailed information about how the data are spread over the interval from the smallest value to the largest value. In general, the pth percentile divides the data set into two parts, where approximately p percent of the observations have values less than the pth percentile and the rest have values greater than the p th percentile. The 25th percentile is also referred to as the first quartile (Ql), the 50th percentile is referred to as the second quartile (Q2), and the 75th percentile is referred to as the third quartile (Q3).

A box plot displays the five-number summary (the smallest value, Q l, Q2, Q3, and the largest value) for the data set. Box plots are particularly useful when comparing similar information gathered at another place or time; they are also an effective tool for identifying outliers. R-96