Basic Analysis and Graphing - SAS

48 Performing Univariate Analysis Chapter 2
Options for Continuous Variables
• The ends of the box represent the 25th and 75th quantiles, also expressed as the 1st and 3rd quartile,
respectively.
• The difference between the 1st and 3rd quartiles is called the interquartile range.
• The box has lines that extend from each end, sometimes called whiskers. The whiskers extend from the
ends of the box to the outermost data point that falls within the distances computed as follows:
1st quartile - 1.5*(interquartile range)
3rd quartile + 1.5*(interquartile range)
If the data points do not reach the computed ranges, then the whiskers are determined by the upper and
lower data point values (not including outliers).
• The bracket outside of the box identifies the shortest half, which is the most dense 50% of the
observations (Rousseuw and Leroy 1987).
Remove Objects from the Outlier Box Plot
To remove the confidence diamond or the shortest half, proceed as follows:
1. Right-click on the outlier box plot and select Customize.
2. Click Box Plot.
3. Deselect the check box next to Confidence Diamond or Shortest Half.
For more details about the Customize Graph window, see the Using JMP book.
Quantile Box Plot
The Quantile Box Plot displays specific quantiles from the Quantiles report. If the distribution is
symmetric, the quantiles in the box plot are approximately equidistant from each other. At a glance, you can
see whether the distribution is symmetric. For example, if the quantile marks are grouped closely at one end,
but have greater spacing at the other end, the distribution is skewed toward the end with more spacing. See
Figure 2.9.