Example 62.2 EDF Statistics and EDF Plot

This example uses the SAS data set Arthritis created in Example 62.1. The data set contains the variable Treatment, which denotes the treatment received by a patient, and the variable Response, which contains the response status of the patient. The variable Freq contains the frequency of the observation, which is the number of patients with the Treatment and Response combination.

The following statements request empirical distribution function (EDF) statistics, which test whether the distribution of a variable is the same across different groups. The EDF option requests the EDF analysis. The variable Treatment is the CLASS variable, and the variable Response specified in the VAR statement is the analysis variable. The FREQ statement names Freq as the frequency variable.

The PLOTS= option requests an EDF plot for Response classified by Treatment. The ODS GRAPHICS ON statement enables ODS Graphics, which is required before requesting plots.

ods graphics on;
proc npar1way edf plots=edfplot data=Arthritis;
   class Treatment;
   var Response;
   freq Freq;
run;
ods graphics off;

Output 62.2.1 shows EDF statistics that compare the two levels of Treatment, Active and Placebo. The asymptotic p-value for the Kolmogorov-Smirnov test is 0.0164. This supports rejection of the null hypothesis that the distributions are the same for the two samples.

Output 62.2.2 shows the EDF plot for Response classified by Treatment.

Output 62.2.2 Empirical Distribution Function Plot