SAS Statistics by Example. Ron Cody, EdD

for subject 55.

      The box plot of the modified data set shows the two outliers as small circles:

      You can even get a bit fancier and let SAS label the outliers:

Program 2.9: Labeling Outliers on a Box Plot

title “Demonstrating How Outliers are Displayed with a Box Plot”; proc sgplot data=Blood_Pressure_Out; hbox SBP / datalabel=Subj; run;

      The option DATALABEL= lets you select a variable to identify specific outliers. If you use the DATALABEL option without naming a label variable, SGPLOT uses the numerical value of the response variable (SBP in this example) to label the outliers. Here is the output:

      Notice that the outliers for subjects 5 and 55 are labeled.

Displaying Multiple Box Plots for Each Value of a Categorical Variable

      If you want to see a box plot for each value of a categorical variable, you can include the option CATEGORY= on the HBOX or VBOX statement. The example that follows uses the original Blood_Pressure data set (without the outliers) and displays a box plot for each value of Drug.

Program 2.10: Displaying Multiple Box Plots for Each Value of a Categorical Variable

title “Box Plots of SBP for Each Value of Drug”; proc sgplot data=example.Blood_Pressure; hbox SBP / category=Drug; run;

      The HBOX option CATEGORY= generates a separate box plot for each of the three Drug values:

Conclusions

      Descriptive statistics should be your first step in data analysis so that you can see a summary of the data and better understand their distribution. This chapter showed you how to produce both numerical and graphical output for continuous variables, using a number of SAS procedures.

      The next two chapters will show you how to display descriptive statistics for categorical variables and how to investigate bivariate relationships.

      Chapter 3 Descriptive Statistics – Categorical Variables

       Introduction

       Computing Frequency Counts and Percentages

       Computing Frequencies on a Continuous Variable

       Using Formats to Group Observations

       Histograms and Bar charts

       Creating a Bar Chart Using PROC SGPLOT