Chapter Contents |
Previous |
Next |
The STEPDISC Procedure |
The following program creates the data set fish and uses PROC STEPDISC to select a subset of potential discriminator variables. By default, PROC STEPDISC uses stepwise selection on all numeric variables that are not listed in other statements, and the significance levels for a variable to enter the subset and to stay in the subset are set to 0.15.
proc format; value specfmt 1='Bream' 2='Roach' 3='Whitefish' 4='Parkki' 5='Perch' 6='Pike' 7='Smelt'; data fish (drop=HtPct WidthPct); title 'Fish Measurement Data'; input Species Weight Length1 Length2 Length3 HtPct WidthPct @@; Height=HtPct*Length3/100; Width=WidthPct*Length3/100; format Species specfmt.; datalines; 1 242.0 23.2 25.4 30.0 38.4 13.4 1 290.0 24.0 26.3 31.2 40.0 13.8 1 340.0 23.9 26.5 31.1 39.8 15.1 1 363.0 26.3 29.0 33.5 38.0 13.3 1 430.0 26.5 29.0 34.0 36.6 15.1 1 450.0 26.8 29.7 34.7 39.2 14.2 1 500.0 26.8 29.7 34.5 41.1 15.3 1 390.0 27.6 30.0 35.0 36.2 13.4 1 450.0 27.6 30.0 35.1 39.9 13.8 1 500.0 28.5 30.7 36.2 39.3 13.7 1 475.0 28.4 31.0 36.2 39.4 14.1 1 500.0 28.7 31.0 36.2 39.7 13.3 1 500.0 29.1 31.5 36.4 37.8 12.0 1 . 29.5 32.0 37.3 37.3 13.6 1 600.0 29.4 32.0 37.2 40.2 13.9 1 600.0 29.4 32.0 37.2 41.5 15.0 1 700.0 30.4 33.0 38.3 38.8 13.8 1 700.0 30.4 33.0 38.5 38.8 13.5 1 610.0 30.9 33.5 38.6 40.5 13.3 1 650.0 31.0 33.5 38.7 37.4 14.8 1 575.0 31.3 34.0 39.5 38.3 14.1 1 685.0 31.4 34.0 39.2 40.8 13.7 1 620.0 31.5 34.5 39.7 39.1 13.3 1 680.0 31.8 35.0 40.6 38.1 15.1 1 700.0 31.9 35.0 40.5 40.1 13.8 1 725.0 31.8 35.0 40.9 40.0 14.8 1 720.0 32.0 35.0 40.6 40.3 15.0 1 714.0 32.7 36.0 41.5 39.8 14.1 1 850.0 32.8 36.0 41.6 40.6 14.9 1 1000.0 33.5 37.0 42.6 44.5 15.5 1 920.0 35.0 38.5 44.1 40.9 14.3 1 955.0 35.0 38.5 44.0 41.1 14.3 1 925.0 36.2 39.5 45.3 41.4 14.9 1 975.0 37.4 41.0 45.9 40.6 14.7 1 950.0 38.0 41.0 46.5 37.9 13.7 2 40.0 12.9 14.1 16.2 25.6 14.0 2 69.0 16.5 18.2 20.3 26.1 13.9 2 78.0 17.5 18.8 21.2 26.3 13.7 2 87.0 18.2 19.8 22.2 25.3 14.3 2 120.0 18.6 20.0 22.2 28.0 16.1 2 0.0 19.0 20.5 22.8 28.4 14.7 2 110.0 19.1 20.8 23.1 26.7 14.7 2 120.0 19.4 21.0 23.7 25.8 13.9 2 150.0 20.4 22.0 24.7 23.5 15.2 2 145.0 20.5 22.0 24.3 27.3 14.6 2 160.0 20.5 22.5 25.3 27.8 15.1 2 140.0 21.0 22.5 25.0 26.2 13.3 2 160.0 21.1 22.5 25.0 25.6 15.2 2 169.0 22.0 24.0 27.2 27.7 14.1 2 161.0 22.0 23.4 26.7 25.9 13.6 2 200.0 22.1 23.5 26.8 27.6 15.4 2 180.0 23.6 25.2 27.9 25.4 14.0 2 290.0 24.0 26.0 29.2 30.4 15.4 2 272.0 25.0 27.0 30.6 28.0 15.6 2 390.0 29.5 31.7 35.0 27.1 15.3 3 270.0 23.6 26.0 28.7 29.2 14.8 3 270.0 24.1 26.5 29.3 27.8 14.5 3 306.0 25.6 28.0 30.8 28.5 15.2 3 540.0 28.5 31.0 34.0 31.6 19.3 3 800.0 33.7 36.4 39.6 29.7 16.6 3 1000.0 37.3 40.0 43.5 28.4 15.0 4 55.0 13.5 14.7 16.5 41.5 14.1 4 60.0 14.3 15.5 17.4 37.8 13.3 4 90.0 16.3 17.7 19.8 37.4 13.5 4 120.0 17.5 19.0 21.3 39.4 13.7 4 150.0 18.4 20.0 22.4 39.7 14.7 4 140.0 19.0 20.7 23.2 36.8 14.2 4 170.0 19.0 20.7 23.2 40.5 14.7 4 145.0 19.8 21.5 24.1 40.4 13.1 4 200.0 21.2 23.0 25.8 40.1 14.2 4 273.0 23.0 25.0 28.0 39.6 14.8 4 300.0 24.0 26.0 29.0 39.2 14.6 5 5.9 7.5 8.4 8.8 24.0 16.0 5 32.0 12.5 13.7 14.7 24.0 13.6 5 40.0 13.8 15.0 16.0 23.9 15.2 5 51.5 15.0 16.2 17.2 26.7 15.3 5 70.0 15.7 17.4 18.5 24.8 15.9 5 100.0 16.2 18.0 19.2 27.2 17.3 5 78.0 16.8 18.7 19.4 26.8 16.1 5 80.0 17.2 19.0 20.2 27.9 15.1 5 85.0 17.8 19.6 20.8 24.7 14.6 5 85.0 18.2 20.0 21.0 24.2 13.2 5 110.0 19.0 21.0 22.5 25.3 15.8 5 115.0 19.0 21.0 22.5 26.3 14.7 5 125.0 19.0 21.0 22.5 25.3 16.3 5 130.0 19.3 21.3 22.8 28.0 15.5 5 120.0 20.0 22.0 23.5 26.0 14.5 5 120.0 20.0 22.0 23.5 24.0 15.0 5 130.0 20.0 22.0 23.5 26.0 15.0 5 135.0 20.0 22.0 23.5 25.0 15.0 5 110.0 20.0 22.0 23.5 23.5 17.0 5 130.0 20.5 22.5 24.0 24.4 15.1 5 150.0 20.5 22.5 24.0 28.3 15.1 5 145.0 20.7 22.7 24.2 24.6 15.0 5 150.0 21.0 23.0 24.5 21.3 14.8 5 170.0 21.5 23.5 25.0 25.1 14.9 5 225.0 22.0 24.0 25.5 28.6 14.6 5 145.0 22.0 24.0 25.5 25.0 15.0 5 188.0 22.6 24.6 26.2 25.7 15.9 5 180.0 23.0 25.0 26.5 24.3 13.9 5 197.0 23.5 25.6 27.0 24.3 15.7 5 218.0 25.0 26.5 28.0 25.6 14.8 5 300.0 25.2 27.3 28.7 29.0 17.9 5 260.0 25.4 27.5 28.9 24.8 15.0 5 265.0 25.4 27.5 28.9 24.4 15.0 5 250.0 25.4 27.5 28.9 25.2 15.8 5 250.0 25.9 28.0 29.4 26.6 14.3 5 300.0 26.9 28.7 30.1 25.2 15.4 5 320.0 27.8 30.0 31.6 24.1 15.1 5 514.0 30.5 32.8 34.0 29.5 17.7 5 556.0 32.0 34.5 36.5 28.1 17.5 5 840.0 32.5 35.0 37.3 30.8 20.9 5 685.0 34.0 36.5 39.0 27.9 17.6 5 700.0 34.0 36.0 38.3 27.7 17.6 5 700.0 34.5 37.0 39.4 27.5 15.9 5 690.0 34.6 37.0 39.3 26.9 16.2 5 900.0 36.5 39.0 41.4 26.9 18.1 5 650.0 36.5 39.0 41.4 26.9 14.5 5 820.0 36.6 39.0 41.3 30.1 17.8 5 850.0 36.9 40.0 42.3 28.2 16.8 5 900.0 37.0 40.0 42.5 27.6 17.0 5 1015.0 37.0 40.0 42.4 29.2 17.6 5 820.0 37.1 40.0 42.5 26.2 15.6 5 1100.0 39.0 42.0 44.6 28.7 15.4 5 1000.0 39.8 43.0 45.2 26.4 16.1 5 1100.0 40.1 43.0 45.5 27.5 16.3 5 1000.0 40.2 43.5 46.0 27.4 17.7 5 1000.0 41.1 44.0 46.6 26.8 16.3 6 200.0 30.0 32.3 34.8 16.0 9.7 6 300.0 31.7 34.0 37.8 15.1 11.0 6 300.0 32.7 35.0 38.8 15.3 11.3 6 300.0 34.8 37.3 39.8 15.8 10.1 6 430.0 35.5 38.0 40.5 18.0 11.3 6 345.0 36.0 38.5 41.0 15.6 9.7 6 456.0 40.0 42.5 45.5 16.0 9.5 6 510.0 40.0 42.5 45.5 15.0 9.8 6 540.0 40.1 43.0 45.8 17.0 11.2 6 500.0 42.0 45.0 48.0 14.5 10.2 6 567.0 43.2 46.0 48.7 16.0 10.0 6 770.0 44.8 48.0 51.2 15.0 10.5 6 950.0 48.3 51.7 55.1 16.2 11.2 6 1250.0 52.0 56.0 59.7 17.9 11.7 6 1600.0 56.0 60.0 64.0 15.0 9.6 6 1550.0 56.0 60.0 64.0 15.0 9.6 6 1650.0 59.0 63.4 68.0 15.9 11.0 7 6.7 9.3 9.8 10.8 16.1 9.7 7 7.5 10.0 10.5 11.6 17.0 10.0 7 7.0 10.1 10.6 11.6 14.9 9.9 7 9.7 10.4 11.0 12.0 18.3 11.5 7 9.8 10.7 11.2 12.4 16.8 10.3 7 8.7 10.8 11.3 12.6 15.7 10.2 7 10.0 11.3 11.8 13.1 16.9 9.8 7 9.9 11.3 11.8 13.1 16.9 8.9 7 9.8 11.4 12.0 13.2 16.7 8.7 7 12.2 11.5 12.2 13.4 15.6 10.4 7 13.4 11.7 12.4 13.5 18.0 9.4 7 12.2 12.1 13.0 13.8 16.5 9.1 7 19.7 13.2 14.3 15.2 18.9 13.6 7 19.9 13.8 15.0 16.2 18.1 11.6 ; proc stepdisc data=fish; class Species; run;
PROC STEPDISC begins by displaying summary information about the analysis; see Figure 60.1. This information includes the number of observations with nonmissing values, the number of classes in the classification variable (specified by the CLASS statement), the number of quantitative variables under consideration, the significance criteria for variables to enter and to stay in the model, and the method of variable selection being used. The frequency of each class is also displayed.
For each entry step, the statistics for entry are displayed for all variables not currently selected; see Figure 60.2. The variable selected to enter at this step (if any) is displayed, as well as all the variables currently selected. Next are multivariate statistics that take into account all previously selected variables and the newly entered variable.
|
For each removal step (Figure 60.3), the statistics for removal are displayed for all variables currently entered. The variable to be removed at this step (if any) is displayed. If no variable meets the criterion to be removed and the maximum number of steps as specified by the MAXSTEP= option has not been attained, then the procedure continues with another entry step.
|
The stepwise procedure terminates either when no variable can be removed and no variable can be entered or when the maximum number of steps as specified by the MAXSTEP= option has been attained. In this example at Step 7 no variables can be either removed or entered (Figure 60.4). Steps 3 through 6 are not displayed in this document.
|
PROC STEPDISC ends by displaying a summary of the steps.
|
All the variables in the data set are found to have potential discriminatory power. These variables are used to develop discrimination models in both the CANDISC and DISCRIM procedure chapters.
Chapter Contents |
Previous |
Next |
Top |
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.