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Example 54.1 Computing a Basic Kernel Density Estimate

This example illustrates the basic functionality of the UNIVAR statement. The effective channel length (in microns) is measured
for 1225 field effect transistors. The channel lengths are saved as values of the variable `length`

in a SAS data set named `channel`

; see the file *kdex1.sas* in the SAS Sample Library. These statements create the `channel`

data set:

data channel;
input length @@;
datalines;
0.91 1.01 0.95 1.13 1.12 0.86 0.96 1.17 1.36 1.10
0.98 1.27 1.13 0.92 1.15 1.26 1.14 0.88 1.03 1.00
0.98 0.94 1.09 0.92 1.10 0.95 1.05 1.05 1.11 1.15
1.11 0.98 0.78 1.09 0.94 1.05 0.89 1.16 0.88 1.19
... more lines ...
2.13 2.05 1.90 2.07 2.15 1.96 2.15 1.89 2.15 2.04
1.95 1.93 2.22 1.74 1.91
;

The following statements request a kernel density estimate of the variable `length`

:

ods graphics on;
proc kde data=channel;
univar length;
run;

Because ODS Graphics is enabled, PROC KDE produces a histogram with an overlaid kernel density estimate by default, although
the PLOTS= option is not specified. The resulting graph is shown in Output 54.1.1. For general information about ODS Graphics, see Chapter 21: Statistical Graphics Using ODS. For specific information about the graphics available in the KDE procedure, see the section ODS Graphics.

Output 54.1.1: Histogram with Overlaid Kernel Density Estimate

The default output tables for this analysis are the "Inputs" and "Controls" tables, shown in Output 54.1.2.

Output 54.1.2: Univariate Inputs Table

The KDE Procedure

WORK.CHANNEL |

1225 |

length |

Sheather-Jones Plug In |

The "Inputs" table lists basic information about the density fit, including the input data set, the number of observations,
the variable used, and the bandwidth method. The default bandwidth method is the Sheather-Jones plug-in.

The "Controls" table lists the primary numbers controlling the kernel density fit. Here the default number of grid points
is used and no adjustment is made to the default bandwidth.