Visualizing Categorical Data: addvar

The addvar macro ( get addvar.sas)

Added variable plots for logistic regression

For a model with a binary response, Y, and predictors in the list X, an added variable plot may be constructed for a new predictor, Z, by plotting the residuals of Y given X against the residuals of Z given X. A linear relation in this plot indicates that Z should be included in the model, but observations with extreme Z-residuals would be highly influential in this decision. A line fitted to this plot should have an intercept approximately zero, and a slope approximating the coefficient of Z in the full model.

The constructed variable plot is designed to detect nonlinear dependence of Y on one of the X variables, say X[j]. It is an added variable plot for the constructed variable, Z = X[j] log X[j].

Method

Usage

The arguments may be listed within parentheses in any order, separated by commas. For example:

  %addvar(data=icu, y=Died,  x=age admit cancer uncons, z=Systolic,
     id=patient, loptions=order=data noprint);

Parameters

DATA=

Specifies the name of the input data set to be analyzed. [Default: DATA=_LAST_]

Y=

Specifies the name of the response variable.

TRIALS=

Name of trials variable for event/trial syntax.

X=

Specifies the names of the predictor variables in the model

Z=

Name of the added variable

ID=

Name of observation ID variable (char)

LOPTIONS=

Options for PROC LOGISTIC [Default: LOPTIONS=NOPRINT]

SMOOTH=

Lowess smoothing parameter [Default: SMOOTH=0.5]

SUBSET=

Subset of points to label [Default: SUBSET=ABS(STUDRES)>2]

OUT=

Specifies the name of the output data set [Default: OUT=_RES_]

SYMBOL=

Plotting symbol for points [Default: SYMBOL=DOT]

INTERP=

Interpolation options for points [Default: INTERP=RL CI=RED]

TYPE=

Type of plot: AVP (for an added-variable plot) or CVP (for a constructed variable plot) [Default: TYPE=AVP]

NAME=

Name of graph in graphic catalog [Default: NAME=ADDVAR]

GOUT=

Name of the graphics catalog

Example

%include vcd(addvar);        *-- or include in an autocall library;
%include data(icu);

  %addvar(data=icu, y=Died,  x=age admit cancer uncons, z=Systolic,
     id=patient, loptions=order=data noprint);

See also