The GENMOD Procedure

PROC GENMOD Statement

PROC GENMOD <options>;

The PROC GENMOD statement invokes the GENMOD procedure. Table 44.1 summarizes the options available in the PROC GENMOD statement.

Table 44.1: PROC GENMOD Statement Options

Option	Description
DATA=	Specifies the input data set
DESCENDING	Sorts response variable in the reverse of the default order
EXACTONLY	Requests only the exact analyses
NAMELEN=	Specifies the length of effect names
ORDER=	Specifies the sort order of CLASS variable
PLOTS	Controls the plots produced through ODS Graphics
RORDER=	Specifies the sort order for the levels of the response variable

You can specify the following options.

DATA=SAS-data-set

specifies the SAS data set containing the data to be analyzed. If you omit the DATA= option, the procedure uses the most recently created SAS data set.

DESCENDING DESCEND DESC

specifies that the levels of the response variable for the ordinal multinomial model and the binomial model with single variable response syntax be sorted in the reverse of the default order. For example, if RORDER=FORMATTED (the default), the DESCENDING option causes the levels to be sorted from highest to lowest instead of from lowest to highest. If RORDER=FREQ, the DESCENDING option causes the levels to be sorted from lowest frequency count to highest instead of from highest to lowest.

EXACTONLY

requests only the exact analyses. The asymptotic analysis that PROC GENMOD usually performs is suppressed.

NAMELEN=n

specifies the length of effect names in tables and output data sets to be n characters long, where n is a value between 20 and 200 characters. The default length is 20 characters.

ORDER=DATA | FORMATTED | FREQ | INTERNAL

specifies the sort order for the levels of the classification variables (which are specified in the CLASS statement).

The ORDER= option can be useful when you use the CONTRAST or ESTIMATE statement because it determines which parameters in the model correspond to each level in the data.

This option applies to the levels for all classification variables, except when you use the (default) ORDER=FORMATTED option with numeric classification variables that have no explicit format. In that case, the levels of such variables are ordered by their internal value.

The ORDER= option can take the following values:

Value of ORDER=	Levels Sorted By
DATA	Order of appearance in the input data set
FORMATTED	External formatted value, except for numeric variables with no explicit format, which are sorted by their unformatted (internal) value
FREQ	Descending frequency count; levels with the most observations come first in the order
INTERNAL	Unformatted value

By default, ORDER=FORMATTED. For ORDER=FORMATTED and ORDER=INTERNAL, the sort order is machine-dependent.

For more information about sort order, see the chapter on the SORT procedure in the Base SAS Procedures Guide and the discussion of BY-group processing in SAS Language Reference: Concepts.

PLOTS <(global-plot-options)> <=plot-request <(options)>> PLOTS <(global-plot-options)> <=(plot-request <(options)> <... plot-request <(options)>>)>

specifies plots to be created using ODS Graphics. Many of the observational statistics in the output data set can be plotted using this option. You are not required to create an output data set in order to produce a plot. When you specify only one plot request, you can omit the parentheses around the plot request. Here are some examples:

plots=all
plots=predicted
plots=(predicted reschi)
plots(unpack)=dfbeta

ODS Graphics must be enabled before plots can be requested. For example:

proc genmod plots=all;
   model y = x;
run;

For more information about enabling and disabling ODS Graphics, see the section Enabling and Disabling ODS Graphics in Chapter 21: Statistical Graphics Using ODS.

Any specified global-plot-options apply to all plots that are specified with plot-requests. The following global-plot-options are available.

CLUSTERLABEL: displays formatted levels of the SUBJECT= effect instead of plot symbols. This option applies only to diagnostic statistics for models fit by GEEs that are plotted against cluster number, and provides a way to identify cluster level names with corresponding ordered cluster numbers.
UNPACK: displays multiple plots individually. The default is to display related multiple plots in a panel.

See the section OUTPUT Statement for definitions of the statistics specified with the plot-requests. The plot-requests include the following:

ALL

produces all available plots.

COOKSD DOBS

plots the Cook’s distance statistic as a function of observation number.

DFBETA

plots the $\bbeta$ deletion statistic as a function of observation number for each regression parameter in the model.

DFBETAS

plots the standardized $\bbeta$ deletion statistic as a function of observation number for each regression parameter in the model.

LEVERAGE

plots the leverage as a function of observation number.

OVERDISP

plots the predicted variance as a function of the predicted mean for a zero-inflated response.

PREDICTED<(option)>

plots predicted values with confidence limits as a function of observation number. The PREDICTED plot request has the following option:

CLM: includes confidence limits in the predicted value plot.

PZERO

plots the zero inflation probability for zero-inflated Poisson and negative binomial models as a function of observation number.

RESCHI<(options)>

The RESCHI plot request has the following options:

INDEX: plots as a function of observation number.
XBETA: plots as a function of linear predictor.

If you do not specify an option, Pearson residuals are plotted as a function of observation number.

RESDEV<(options)>

plots deviance residuals. The RESDEV plot request has the following options:

INDEX: plots as a function of observation number.
XBETA: plots as a function of linear predictor.

If you do not specify an option, deviance residuals are plotted as a function of observation number.

RESLIK<(options)>

plots likelihood residuals. The RESLIK plot request has the following options:

INDEX: plots as a function of observation number.
XBETA: plots as a function of linear predictor.

If you do not specify an option, likelihood residuals are plotted as a function of observation number.

RESRAW<(options)>

plots raw residuals. The RESRAW plot request has the following options:

INDEX: plots as a function of observation number.
XBETA: plots as a function of linear predictor.

If you do not specify an option, raw residuals are plotted as a function of observation number.

STDRESCHI<(options)>

plots standardized Pearson residuals. The STDRESCHI plot request has the following options:

INDEX: plots as a function of observation number.
XBETA: plots as a function of linear predictor.

If you do not specify an option, standardized Pearson residuals are plotted as a function of observation number.

STDRESDEV<(options)>

plots standardized deviance residuals. The STDRESDEV plot request has the following options:

INDEX: plots as a function of observation number.
XBETA: plots as a function of linear predictor.

If you do not specify an option, standardized deviance residuals are plotted as a function of observation number.

If you fit a model by using generalized estimating equations (GEEs), the following additional plot-requests are available:

CLEVERAGE: plots the cluster leverage as a function of ordered cluster.
CLUSTERCOOKSD DCLS: plots the cluster Cook’s distance statistic as a function of ordered cluster.
CLUSTERDFIT MCLS: plots the studentized cluster Cook’s distance statistic as a function of ordered cluster.
DFBETAC: plots the cluster deletion statistic as a function of ordered cluster for each regression parameter in the model.
DFBETACS: plots the standardized cluster deletion statistic as a function of ordered cluster for each regression parameter in the model.

RORDER=keyword

specifies the sort order for the levels of the response variable. This order determines which intercept parameter in the model corresponds to each level in the data. If RORDER=FORMATTED for numeric variables for which you have supplied no explicit format, the levels are ordered by their internal values. The following table displays the valid keywords and describes how PROC GENMOD interprets them.

RORDER=keyword	Levels Sorted by
DATA	Order of appearance in the input data set
FORMATTED	External formatted value, except for numeric
	variables with no explicit format, which are
	sorted by their unformatted (internal) value
FREQ	Descending frequency count; levels with the
	most observations come first in the order
INTERNAL	Unformatted value

By default, RORDER=FORMATTED. For RORDER=FORMATTED and RORDER=INTERNAL, the sort order is machine dependent. The DESCENDING option in the PROC GENMOD statement causes the response variable to be sorted in the reverse of the order displayed in the previous table. For more information about sort order, see the chapter on the SORT procedure in the Base SAS Procedures Guide.

The NOPRINT option, which suppresses displayed output in other SAS procedures, is not available in the PROC GENMOD statement. However, you can use the Output Delivery System (ODS) to suppress all displayed output, store all output on disk for further analysis, or create SAS data sets from selected output. You can suppress all displayed output with the statement ODS SELECT NONE; and turn displayed output back on with the statement ODS SELECT ALL;. See Table 44.12 and Table 44.13 for the names of output tables available from PROC GENMOD. For more information about ODS, see Chapter 20: Using the Output Delivery System.