The LOGISTIC Procedure

specifies the level of significance for % confidence intervals. The value number must be between 0 and 1; the default value is 0.05, which results in 95% intervals. This value is used as the default confidence level for limits computed by the following options:

You can override the default in most of these cases by specifying the ALPHA= option in the separate statements.

adds the estimated covariance matrix to the OUTEST= data set. For the COVOUT option to have an effect, the OUTEST= option must be specified. See the section OUTEST= Output Data Set for more information.

names 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. The INMODEL= option cannot be specified with this option.

reverses the sorting order for the levels of the response variable. If both the DESCENDING and ORDER= options are specified, PROC LOGISTIC orders the levels according to the ORDER= option and then reverses that order. This option has the same effect as the response variable option DESCENDING in the MODEL statement. See the section Response Level Ordering for more detail.

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

specifies options that apply to every EXACT statement in the program. The available options are summarized here, and full descriptions are available in the EXACTOPTIONS statement.

names the SAS data set that contains initial estimates for all the parameters in the model. If BY-group processing is used, it must be accommodated in setting up the INEST= data set. See the section INEST= Input Data Set for more information.

specifies the name of the SAS data set that contains the model information needed for scoring new data. This INMODEL= data set is the OUTMODEL= data set saved in a previous PROC LOGISTIC call. The OUTMODEL= data set should not be modified before its use as an INMODEL= data set.

The DATA= option cannot be specified with this option; instead, specify the data sets to be scored in the SCORE statements. FORMAT statements are not allowed when the INMODEL= data set is specified; variables in the DATA= and PRIOR= data sets in the SCORE statement should be formatted within the data sets.

You can specify the BY statement provided that the INMODEL= data set is created under the same BY-group processing.

The CLASS, EFFECT, EFFECTPLOT, ESTIMATE, EXACT, LSMEANS, LSMESTIMATE, MODEL, OUTPUT, ROC, ROCCONTRAST, SLICE, STORE, TEST, and UNIT statements are not available with the INMODEL= option.

forces the procedure to reread the DATA= data set as needed rather than require its storage in memory or in a temporary file on disk. By default, the data set is cleaned up and stored in memory or in a temporary file. This option can be useful for large data sets. All exact analyses are ignored in the presence of the MULTIPASS option. If a STRATA statement is specified, then the data set must first be grouped or sorted by the strata variables.

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

specifies that the covariance matrix not be saved in the OUTMODEL= data set. The covariance matrix is needed for computing the confidence intervals for the posterior probabilities in the OUT= data set in the SCORE statement. Specifying this option will reduce the size of the OUTMODEL= data set.

suppresses all displayed output. Note that this option temporarily disables the Output Delivery System (ODS); see Chapter 20, Using the Output Delivery System, for more information.

specifies the sorting order for the levels of the response variable. See the response variable option ORDER= in the MODEL statement for more information. For ordering of CLASS variable levels, see the ORDER= option in the CLASS statement.

specifies the name of the data set that contains the design matrix for the model. The data set contains the same number of observations as the corresponding DATA= data set and includes the response variable (with the same format as in the DATA= data set), the FREQ variable, the WEIGHT variable, the OFFSET= variable, and the design variables for the covariates, including the Intercept variable of constant value 1 unless the NOINT option in the MODEL statement is specified.

suppresses the model fitting and creates only the OUTDESIGN= data set. This option is ignored if the OUTDESIGN= option is not specified.

creates an output SAS data set that contains the final parameter estimates and, optionally, their estimated covariances (see the preceding COVOUT option). The output data set also includes a variable named _LNLIKE_, which contains the log likelihood. See the section OUTEST= Output Data Set for more information.

specifies the name of the SAS data set that contains the information about the fitted model. This data set contains sufficient information to score new data without having to refit the model. It is solely used as the input to the INMODEL= option in a subsequent PROC LOGISTIC call. The OUTMODEL= option is not available with the STRATA statement. Information in this data set is stored in a very compact form, so you should not modify it manually.

Note: The STORE statement can also be used to save your model. See the section STORE Statement for more information.

controls the plots produced through ODS Graphics. When you specify only one plot-request, you can omit the parentheses from around the plot-request. For example:

PLOTS = ALL
PLOTS = (ROC EFFECT INFLUENCE(UNPACK))
PLOTS(ONLY) = EFFECT(CLBAR SHOWOBS)

ODS Graphics must be enabled before requesting plots. For example:

ods graphics on;
proc logistic plots=all;
   model y=x;
run;
ods graphics off;

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

If the PLOTS option is not specified or is specified with no plot-requests, then graphics are produced by default in the following situations:

• If the INFLUENCE or IPLOTS option is specified in the MODEL statement, then the line-printer plots are suppressed, and the INFLUENCE plots are produced unless the MAXPOINTS= cutoff is exceeded.

• If you specify the OUTROC= option in the MODEL statement, then ROC curves are produced. If you also specify a SELECTION= method, then an overlaid plot of all the ROC curves for each step of the selection process is displayed.

• If the OUTROC= option is specified in a SCORE statement, then the ROC curve for the scored data set is displayed.

• If you specify ROC statements, then an overlaid plot of the ROC curves for the model (or the selected model if a SELECTION= method is specified) and for all the ROC statement models is displayed.

• If you specify the CLODDS= option in the MODEL statement, or specify an ODDSRATIO statement, then a plot of the odds ratios and their confidence limits is displayed.

For general information about ODS Graphics, see Chapter 21, Statistical Graphics Using ODS.

The following global-plot-options are available:

LABEL

displays the case number on diagnostic plots, to aid in identifying the outlying observations. This option enhances the plots produced by the DFBETAS, DPC, INFLUENCE, LEVERAGE, and PHAT options.

MAXPOINTS=NONE | number

suppresses the plots produced by the DFBETAS, DPC, INFLUENCE, LEVERAGE, and PHAT options if there are more than number observations. Also, observations are not displayed on the EFFECT plots when the cutoff is exceeded. The default is MAXPOINTS=5000. The cutoff is ignored if you specify MAXPOINTS=NONE.

ONLY

suppresses the default plots. Only specifically requested plot-requests are displayed.

UNPACKPANELS | UNPACK

suppresses paneling. By default, multiple plots can appear in some output panels. Specify UNPACKPANEL to display each plot separately.

The following plot-requests are available:

ALL

produces all appropriate plots. You can specify other options with ALL. For example, to display all plots and unpack the DFBETAS plots you can specify plots=(all dfbetas(unpack)).

DFBETAS <(UNPACK)>

displays plots of DFBETAS versus the case (observation) number. This displays the statistics generated by the DFBETAS=_ALL_ option in the OUTPUT statement. The UNPACK option displays the plots separately. See Output 53.6.5 for an example of this plot.

DPC<(UNPACK)>

displays plots of DIFCHISQ and DIFDEV versus the predicted event probability, and colors the markers according to the value of the confidence interval displacement C. The UNPACK option displays the plots separately. See Output 53.6.8 for an example of this plot.

EFFECT<(effect-options)>

displays and enhances the effect plots for the model. For more information about effect plots and the available effect-options, see the section PLOTS=EFFECT Plots.

Note: The EFFECTPLOT statement provides you with much of the same functionality and more options for creating effect plots. See Outputs 53.2.11, 53.3.5, 53.4.8, 53.7.4, and 53.15.4 for examples of effect plots.

INFLUENCE<(UNPACK | STDRES)>

displays index plots of RESCHI, RESDEV, leverage, confidence interval displacements C and CBar, DIFCHISQ, and DIFDEV. These plots are produced by default when any plot-request is specified and the MAXPOINTS= cutoff is not exceeded. The UNPACK option displays the plots separately. The STDRES option also displays index plots of STDRESCHI, STDRESDEV, and RESLIK. See Outputs 53.6.3 and 53.6.4 for examples of these plots.

LEVERAGE<(UNPACK)>

displays plots of DIFCHISQ, DIFDEV, confidence interval displacement C, and the predicted probability versus the leverage. The UNPACK option displays the plots separately. See Output 53.6.7 for an example of this plot.

NONE

suppresses all plots.

ODDSRATIO<(oddsratio-options)>

displays and enhances the odds ratio plots for the model when the CLODDS= option or ODDSRATIO statements are also specified. For more information about odds ratio plots and the available oddsratio-options, see the section Odds Ratio Plots. See Outputs 53.7,53.2.9, 53.3.3, and 53.4.5 for examples of this plot.

PHAT<(UNPACK)>

displays plots of DIFCHISQ, DIFDEV, confidence interval displacement C, and leverage versus the predicted event probability. The UNPACK option displays the plots separately. See Output 53.6.6 for an example of this plot.

ROC<(ID=keyword)>

displays the ROC curve. If you also specify a SELECTION= method, then an overlaid plot of all the ROC curves for each step of the selection process is displayed. If you specify ROC statements, then an overlaid plot of the model (or the selected model if a SELECTION= method is specified) and the ROC statement models will be displayed. If the OUTROC= option is specified in a SCORE statement, then the ROC curve for the scored data set is displayed.

The ID= option labels certain points on the ROC curve. Typically, the labeled points are closest to the upper-left corner of the plot, and points directly below or to the right of a labeled point are suppressed. Specifying ID=PROB | CUTPOINT displays the predicted probability of those points, while ID=CASENUM | OBS displays the observation number. In case of ties, only the last observation number is displayed.

See Output 53.7.3 and Example 53.8 for examples of these ROC plots.

specifies options that apply to every model specified in a ROC statement. The following options are available:

ALPHA=number

sets the significance level for creating confidence limits of the areas and the pairwise differences. The ALPHA= value specified in the PROC LOGISTIC statement is the default. If neither ALPHA= value is specified, then ALPHA=0.05 by default.

EPS=value

is an alias for the ROCEPS= option in the MODEL statement. This value is used to determine which predicted probabilities are equal. The default value is the square root of the machine epsilon, which is about 1E–8.

ID=keyword-or-variable

displays labels on certain points on the individual ROC curves. This option is identical to, and overrides, the ID= suboption of the PLOTS=ROC option in the PROC statement. Specifying ID=PROB | CUTPOINT displays the predicted probability of an observation, while ID=CASENUM | OBS displays the observation number. In case of ties, the last observation number is displayed.

NODETAILS

suppresses the display of the model fitting information for the models specified in the ROC statements.

OUT=SAS-data-set-name

is an alias for the OUTROC= option in the MODEL statement.

WEIGHTED

uses frequencyweight in the ROC computations (Izrael et al.; 2002) instead of just frequency. Typically, weights are considered in the fit of the model only, and hence are accounted for in the parameter estimates. The "Association of Predicted Probabilities and Observed Responses" table uses frequency only, and is suppressed when ROC comparisons are performed.

displays simple descriptive statistics (mean, standard deviation, minimum and maximum) for each continuous explanatory variable. For each CLASS variable involved in the modeling, the frequency counts of the classification levels are displayed. The SIMPLE option generates a breakdown of the simple descriptive statistics or frequency counts for the entire data set and also for individual response categories.

determines class levels by using no more than the first 16 characters of the formatted values of CLASS, response, and strata variables. When formatted values are longer than 16 characters, you can use this option to revert to the levels as determined in releases previous to SAS 9.0. This option invokes the same option in the CLASS statement.