# SAS Macro Programs: `inflogis`

$Version: 1.3 (20 Mar 2003)

**
Michael Friendly**

York University

### Influence plots for logistic regression

The `INFLOGIS` macro produces influence plots for a logistic
regression model. The plot shows a measure of badness of fit for a
given case (DIFDEV or DIFCHISQ) vs. the fitted probability (PRED)
or leverage (HAT), using an influence measure (C or CBAR) as the
size of a bubble.
### Method

The macro fits the logistic model and
obtains an output data set containing the diagnostic quantities
which are plotted.
## Usage

`inflogis` is a macro program. Values must be supplied for the Y=
and X= parameters.
The arguments may be listed within parentheses in any order, separated
by commas. For example:

%inflogis(Y=responsevar, X=independentvars, ..., )

### Parameters

- Y=
- Name of criterion variable
- X=
- Names of predictors
- ID=
- Name of observation ID variable (char)
- DATA=_LAST_
- The name of the input dataset. If not specified, the most
recently created dataset is used.
- GY=DIFDEV
- Ordinate for plot: Specify one or more of DIFDEV or DIFCHISQ
- GX=PRED
- Abscissa for plot: PRED or HAT
- BUBBLE=C
- Influence measure the bubble is made
proportional to: specify either BUBBLE=C or CBAR
- LABEL=INFL
- Points to be labelled with the value of the
ID variable in the plot: ALL, NONE, or
INFL. The choice INFL causes only influential points to be
labelled.
- LSIZE=1.5
- Observation label size. The height of
other text (axis labels, etc.) is controlled by
the HTEXT= goption
- LCOLOR=BLACK
- Observation label color
- LPOS=5
- Observation label position, using the position values
understood by the Annotate facility.
- BSIZE=10
- bubble size scale factor
- BSCALE=AREA
- Sacle for the bubble size. AREA makes the
bubble area proportional to the influence measure; RADIUS makes the bubble
radius proportional to influence.
- BCOLOR=BLACK
- bubble color
- REFCOL=BLACK
- color of reference lines
- REFLIN=33
- line style for reference lines; 0->NONE
- LOPTIONS=NOPRINT
- Additional options for PROC LOGISTIC
- NAME=INFLOGIS
- Name for graphic catalog entry
- GOUT=
- Name of graphics catalog

### Example

The example below displays an influence plot for a logistic
regression model predicting outcome of a treatment for
arthritis pain, based on Sex, Treatment, and Age.
The plots display the Chi-square difference
when the observation is deleted vs. both thepredicted probability of succesful
outcome and the leverage
with the bubble size proportional to the Cook's D measure of influence.

%include macros(inflogis); *-- or include in an autocall library;
%include data(arthrit);
%inflogis(data=arthrit,
y=better,
x=_sex_ _treat_ age,
id=case,
gy=DIFCHISQ,
gx=PRED HAT,
lcolor=RED, bsize=14
);

### See also

dummy Construct dummy variables for regression models

inflplot Influence plot for regression models