PROC GENMOD: ASSESS Statement :: SAS/STAT(R) 9.2 User's Guide, Second Edition

The GENMOD Procedure

ASSESS Statement

ASSESS VAR=(effect) | LINK </ options> ;

ASSESSMENT VAR=(effect) | LINK </ options> ;

The ASSESS statement computes and plots, using ODS Graphics, model-checking statistics based on aggregates of residuals. See the section Assessment of Models Based on Aggregates of Residuals for details about the model assessment methods available in GENMOD.

The types of aggregates available are cumulative residuals, moving sums of residuals, and loess smoothed residuals. If you do not specify which aggregate to use, the assessments are based on cumulative sums. PROC GENMOD uses ODS Graphics for graphical displays. For specific information about the graphics available in PROC GENMOD, see the section ODS Graphics.

You must specify either LINK or VAR= in order to create an analysis.

LINK requests the assessment of the link function by performing the analysis with respect to the linear predictor.

VAR=(effect) specifies that the functional form of a covariate be checked by performing the analysis with respect to the variable identified by the effect. The effect must be specified in the MODEL statement and must contain only continuous variables (variables not listed in a CLASS statement).

You can specify the following options after the slash (/).

CRPANEL: requests that a plot with four panels showing just a few of the paths from the default aggregate plot to make it easier to compare simulated and observed paths. The plot in each panel contains aggregates of the observed residuals and two simulated curves (fewer if NPATHS= is less than 8).
LOESS<(number)>
LOWESS<(number)>: requests model assessment based on loess smoothed residuals with optional number the fraction of data used; number must be between zero and one. If number is not specified, the default value one-third is used.
NPATHS=number
NPATH=number
PATHS=number
PATH=number: specifies the number of simulated paths to plot in the default aggregate residuals plot. The default value of number is twenty.
RESAMPLE<=number>
RESAMPLES<=number>: specifies that a p-value be computed based on 1,000 simulated paths, or number paths, if number is specified.
SEED=number: specifies a seed for the normal random number generator used in creating simulated realizations of aggregates of residuals for plots and estimating $\text{[math]}$ -values. Specifying a seed enables you to produce identical graphs and $\text{[math]}$ -values from one run of the procedure to the next run. If a seed is not specified, or if number is negative or zero, a random number seed is derived from the time of day.
WINDOW<(number)>: requests assessment based on a moving sum window of width number. If number is not specified, a value of one-half of the range of the x-coordinate is used.

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