The PROBIT Procedure
 IPPPLOT Statement
IPPPLOT <var = variable> <options> ;

The IPPPLOT statement plots the inverse of the predicted probability (IPP) against a single continuous variable (dose variable) in the MODEL statement for the binomial model. You can only use this statement after a binomial model statement. The confidence limits for the predicted values of the dose variable are the computed fiducial limits, not the inverse of the confidence limits of the predicted probabilities. Refer to the section Inverse Confidence Limits for more details.

VAR= variable

specifies a single continuous variable (dose variable) in the independent variable list of the MODEL statement. If a VAR= variable is not specified, the first single continuous variable in the independent variable list of the MODEL statement is used. If such a variable does not exist in the independent variable list of the MODEL statement, an error is reported.

For the binomial model, the response variable is a probability. An estimate of the dose level needed for a response of is given by

where is the cumulative distribution function used to model the probability, is the vector of the rest of the covariates, is the vector of the estimated parameters corresponding to , and is the estimated parameter for the dose variable of interest.

To plot as a function of , must be specified. You can use the XDATA= option to provide the values of (see the XDATA= option in the PROC PROBIT statement for details), or use the default values that follow the rules:

• If the effect contains a continuous variable (or variables), the overall mean of this effect is used.

• If the effect is a single classification variable, the highest level of the variable is used.

options

You can use options in the IPPPLOT statement to do the following:

• superimpose specification limits

• suppress or add the observed data points on the plot

• suppress or add the fiducial limits on the plot

• specify graphical enhancements (such as color or text height)

### Summary of Options

Table 72.12 through Table 72.18 list all options by function. The Dictionary of Options describes each option in detail.

#### IPP Options

 NOCONF Suppresses fiducial limits NODATA Suppresses observed data points on the plot NOTHRESH Suppresses the threshold line THRESHLABPOS=value Specifies the position for the label of the threshold line

#### General Options

 CAXIS=color Specifies color for axis CFIT=color Specifies color for fitted curves CFRAME=color Specifies color for frame CGRID=color Specifies color for grid lines CHREF=color Specifies color for HREF= lines CTEXT=color Specifies color for text CVREF=color Specifies color for VREF= lines
 ANNOTATE=SAS-data-set Specifies an Annotate data set INBORDER Requests a border around plot LFIT=linetype Specifies line style for fitted curves and confidence limits LGRID=linetype Specifies line style for grid lines NOFRAME Suppresses the frame around plotting areas NOGRID Suppresses grid lines NOFIT Suppresses fitted curves NOHLABEL Suppresses horizontal labels NOHTICK Suppresses horizontal ticks NOVTICK Suppresses vertical ticks TURNVLABELS Vertically strings out characters in vertical labels WFIT=n Specifies thickness for fitted curves WGRID=n Specifies thickness for grids WREFL=n Specifies thickness for reference lines
 HAXIS=value1 to value2 Specifies tick mark values for horizontal axis HOFFSET=value Specifies offset for horizontal axis HLOWER=value Specifies lower limit on horizontal axis scale HUPPER=value Specifies upper limit on horizontal axis scale NHTICK=n Specifies number of ticks for horizontal axis NVTICK=n Specifies number of ticks for vertical axis VAXIS=value1 to value2 Specifies tick mark values for vertical axis VAXISLABEL=’label’ Specifies label for vertical axis VOFFSET=value Specifies offset for vertical axis VLOWER=value Specifies lower limit on vertical axis scale VUPPER=value Specifies upper limit on vertical axis scale WAXIS=n Specifies thickness for axis
 HREF<(INTERSECT)>=value-list Requests horizontal reference line HREFLABELS=(’label1’,...,’labeln’) Specifies labels for HREF= lines HREFLABPOS= Specifies vertical position of labels for HREF= lines LHREF=linetype Specifies line style for HREF= lines LVREF=linetype Specifies line style for VREF= lines VREF<(INTERSECT)>=value-list Requests vertical reference line VREFLABELS=(’label1’,...,’labeln’) Specifies labels for VREF= lines VREFLABPOS= Specifies horizontal position of labels for VREF= lines
 DESCRIPTION=’string’ Specifies description for graphics catalog member NAME=’string’ Specifies name for plot in graphics catalog
 FONT=font Specifies software font for text HEIGHT=value Specifies height of text used outside framed areas INFONT=font Specifies software font for text inside framed areas INHEIGHT=value Specifies height of text inside framed areas

### Dictionary of Options

The following entries provide detailed descriptions of the options in the IPPPLOT statement.

ANNOTATE=SAS-data-set
ANNO=SAS-data-set

specifies an Annotate data set, as described in SAS/GRAPH Software: Reference, that enables you to add features to the IPP plot. The ANNOTATE= data set you specify in the IPPPLOT statement is used for all plots created by the statement.

CAXIS=color
CAXES=color

specifies the color used for the axes and tick marks. This option overrides any COLOR= specifications in an AXIS statement. The default is the first color in the device color list.

CFIT=color

specifies the color for the fitted IPP curves. The default is the first color in the device color list.

CFRAME=color
CFR=color

specifies the color for the area enclosed by the axes and frame. This area is not shaded by default.

CGRID=color

specifies the color for grid lines. The default is the first color in the device color list.

CHREF=color
CH=color

specifies the color for lines requested by the HREF= option. The default is the first color in the device color list.

CTEXT=color

specifies the color for tick mark values and axis labels. The default is the color specified for the CTEXT= option in the most recent GOPTIONS statement.

CVREF=color
CV=color

specifies the color for lines requested by the VREF= option. The default is the first color in the device color list.

DESCRIPTION=’string’
DES=’string’

specifies a description, up to 40 characters, that appears in the PROC GREPLAY master menu. The default is the variable name.

FONT=font

specifies a software font for reference line and axis labels. You can also specify fonts for axis labels in an AXIS statement. The FONT= font takes precedence over the FTEXT= font specified in the most recent GOPTIONS statement. Hardware characters are used by default.

HAXIS=value1 to value2 <by value3>

specifies tick mark values for the horizontal axis; value1, value2, and value3 must be numeric, and value1 must be less than value2. The lower tick mark is value1. Tick marks are drawn at increments of value3. The last tick mark is the greatest value that does not exceed value2. If value3 is omitted, a value of 1 is used.

Examples of HAXIS= lists follow:

```   haxis = 0 to 10
haxis = 2 to 10 by 2
haxis = 0 to 200 by 10
```
HEIGHT=value

specifies the height of text used outside framed areas. The default value is 3.846 (in percentage).

HLOWER=value

specifies the lower limit on the horizontal axis scale. The HLOWER= option specifies value as the lower horizontal axis tick mark. The tick mark interval and the upper axis limit are determined automatically. This option has no effect if the HAXIS= option is used.

HOFFSET=value

specifies offset for horizontal axis. The default value is 1.

HUPPER=value

specifies value as the upper horizontal axis tick mark. The tick mark interval and the lower axis limit are determined automatically. This option has no effect if the HAXIS= option is used.

HREF <(INTERSECT)> =value-list

requests reference lines perpendicular to the horizontal axis. If (INTERSECT) is specified, a second reference line perpendicular to the vertical axis is drawn that intersects the fit line at the same point as the horizontal axis reference line. If a horizontal axis reference line label is specified, the intersecting vertical axis reference line is labeled with the vertical axis value. See also the CHREF=, HREFLABELS=, and LHREF= options.

HREFLABELS=’label1’,...,’labeln’
HREFLABEL=’label1’,...,’labeln’
HREFLAB=’label1’,...,’labeln’

specifies labels for the lines requested by the HREF= option. The number of labels must equal the number of lines. Enclose each label in quotes. Labels can be up to 16 characters.

HREFLABPOS=

specifies the vertical position of labels for HREF= lines. The following table shows valid values for n and the corresponding label placements.

 n label placement 1 Top 2 Staggered from top 3 Bottom 4 Staggered from bottom 5 Alternating from top 6 Alternating from bottom
INBORDER

requests a border around IPP plots.

LFIT=linetype

specifies a line style for fitted curves and confidence limits. By default, fitted curves are drawn by connecting solid lines (linetype = 1) and confidence limits are drawn by connecting dashed lines (linetype = 3).

LGRID=linetype

specifies a line style for all grid lines. The value for linetype must be between 1 and 46. The default is 35.

LHREF=linetype
LH=linetype

specifies the line type for lines requested by the HREF= option. The default is 2, which produces a dashed line.

LVREF=linetype
LV=linetype

specifies the line type for lines requested by the VREF= option. The default is 2, which produces a dashed line.

NAME=’string’

specifies a name for the plot, up to eight characters, that appears in the PROC GREPLAY master menu. The default is ’PROBIT’.

NOCONF

suppresses fiducial limits from the plot.

NODATA

suppresses observed data points from the plot.

NOFIT

suppresses the fitted IPP curves.

NOFRAME

suppresses the frame around plotting areas.

NOGRID

suppresses grid lines.

NOHLABEL

suppresses horizontal labels.

NOHTICK

suppresses horizontal tick marks.

NOTHRESH

suppresses the threshold line.

NOVLABEL

suppresses vertical labels.

NOVTICK

suppresses vertical tick marks.

THRESHLABPOS=

specifies the vertical position of labels for the threshold line. The following table shows valid values for n and the corresponding label placements.

 n label placement 1 Top 2 Bottom
VAXIS=value1 to value2 <by value3>

specifies tick mark values for the vertical axis; value1, value2, and value3 must be numeric, and value1 must be less than value2. The lower tick mark is value1. Tick marks are drawn at increments of value3. The last tick mark is the greatest value that does not exceed value2. This method of specification of tick marks is not valid for logarithmic axes. If value3 is omitted, a value of 1 is used.

Examples of VAXIS= lists follow:

```   vaxis = 0 to 10
vaxis = 0 to 2 by .1
```
VAXISLABEL=’string’

specifies a label for the vertical axis.

VLOWER=value

specifies the lower limit on the vertical axis scale. The VLOWER= option specifies value as the lower vertical axis tick mark. The tick mark interval and the upper axis limit are determined automatically. This option has no effect if the VAXIS= option is used.

VREF=value-list

requests reference lines perpendicular to the vertical axis. If (INTERSECT) is specified, a second reference line perpendicular to the horizontal axis is drawn that intersects the fit line at the same point as the vertical axis reference line. If a vertical axis reference line label is specified, the intersecting horizontal axis reference line is labeled with the horizontal axis value. See also the CVREF=, LVREF=, and VREFLABELS= options.

VREFLABELS=’label1’,...,’labeln’
VREFLABEL=’label1’,...,’labeln’
VREFLAB=’label1’,...,’labeln’

specifies labels for the lines requested by the VREF= option. The number of labels must equal the number of lines. Enclose each label in quotes. Labels can be up to 16 characters.

VREFLABPOS=

specifies the horizontal position of labels for VREF= lines. The following table shows valid values for n and the corresponding label placements.

 n label placement 1 Left 2 Right
VUPPER=value

specifies the upper limit on the vertical axis scale. The VUPPER= option specifies value as the upper vertical axis tick mark. The tick mark interval and the lower axis limit are determined automatically. This option has no effect if the VAXIS= option is used.

WAXIS=

specifies line thickness for axes and frame. The default value is 1.

WFIT=

specifies line thickness for fitted curves. The default value is 1.

WGRID=

specifies line thickness for grids. The default value is 1.

WREFL=

specifies line thickness for reference lines. The default value is 1.

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