The REG Procedure 
PLOT Statement 
The PLOT statement in PROC REG displays scatter plots with yvariable on the vertical axis and xvariable on the horizontal axis. Line printer plots are generated if the LINEPRINTER option is specified in the PROC REG statement; otherwise, the traditional graphics are created. Points in line printer plots can be marked with symbols, while global graphics statements such as GOPTIONS and SYMBOL are used to enhance the traditional graphics. Note that the plots you request by using the PLOT statement are independent of the ODS graphical displays (see the section ODS Graphics) that are now available in PROC REG.
As with most other interactive statements, the PLOT statement implicitly refits the model. For example, if a PLOT statement is preceded by a REWEIGHT statement, the model is recomputed, and the plot reflects the new model.
If there are multiple MODEL statements preceding a PLOT statement, then the PLOT statement refers to the latest MODEL statement.
The PLOT statement cannot be used when a TYPE=CORR, TYPE=COV, or TYPE=SSCP data set is used as input to PROC REG.
You can specify several PLOT statements for each MODEL statement, and you can specify more than one plot in each PLOT statement.
For detailed examples of using the PLOT statement and its options, see the section Producing Scatter Plots.
More than one yvariablexvariable pair can be specified to request multiple plots. The yvariables and xvariables can be as follows:
any variables specified in the VAR or MODEL statement before the first RUN statement
keyword., where keyword is a regression diagnostic statistic available in the OUTPUT statement (see Table 74.6). For example,
plot predicted.*residual.;
generates one plot of the predicted values by the residuals for each dependent variable in the MODEL statement. These statistics can also be plotted against any of the variables in the VAR or MODEL statements.
the keyword OBS. (the observation number), which can be plotted against any of the preceding variables
the keyword NPP. or NQQ., which can be used with any of the preceding variables to construct normal PP or QQ plots, respectively (see the section Construction of QQ and PP Plots and Traditional Normal Quantile and Normal Probability Plots for more information)
keywords for model fit summary statistics available in the OUTEST= data set with _TYPE_= PARMS (see Table 74.6). A SELECTION= method (other than NONE) must be requested in the MODEL statement for these variables to be plotted. If one member of a yvariablexvariable pair is from the OUTEST= data set, the other member must also be from the OUTEST= data set.
The OUTPUT statement and the OUTEST= option are not required when their keywords are specified in the PLOT statement.
The yvariable and xvariable specifications can be replaced by a set of variables and statistics enclosed in parentheses. When this occurs, all possible combinations of yvariable and xvariable are generated. For example, the following two statements are equivalent:
plot (y1 y2)*(x1 x2); plot y1*x1 y1*x2 y2*x1 y2*x2;
The statement
plot;
is equivalent to respecifying the most recent PLOT statement without any options. However, the line printer options COLLECT, HPLOTS=, SYMBOL=, and VPLOTS=, described in the section Line Printer Plots, apply across PLOT statements and remain in effect if they have been previously specified.
Options used for the traditional graphics are described in the following section; see Line Printer Plots for more information.
The display of traditional graphics is described in the following paragraphs, the options are summarized in Table 74.6 and described in the section "Dictionary of PLOT Statement Options", and the section Traditional Graphics contains several examples of the graphics output.
Several line printer statements and options are not supported for the traditional graphics. In particular the PAINT statement is disabled, as are the PLOT statement options CLEAR, COLLECT, HPLOTS=, NOCOLLECT, SYMBOL=, and VPLOTS=. To display more than one plot per page or to collect plots from multiple PLOT statements, use the PROC GREPLAY statement (refer to SAS/GRAPH Software: Reference). Also note that traditional graphics options are not recognized for line printer plots.
The fitted model equation and a label are displayed in the top margin of the plot; this display can be suppressed with the NOMODEL option. If the label is requested but cannot fit on one line, it is not displayed. The equation and label are displayed on one line when possible; if more lines are required, the label is displayed in the first line with the model equation in successive lines. If displaying the entire equation causes the plot to be unacceptably small, the equation is truncated. Table 74.7 lists options to control the display of the equation. The section Traditional Graphics for Simple Linear Regression illustrates the display of the model equation.
Four statistics are displayed by default in the right margin: the number of observations, , the adjusted , and the root mean square error. (See Figure 74.43.) The display of these statistics can be suppressed with the NOSTAT option. You can specify other options to request the display of various statistics in the right margin; see Table 74.7.
A default reference line at zero is displayed if residuals are plotted. If the dependent variable is plotted against the independent variable in a simple linear regression model, the fitted regression line is displayed by default. (See Figure .) Default reference lines can be suppressed with the NOLINE option; the lines are not displayed if the OVERLAY option is specified.
Specialized plots are requested with special options. For each coefficient, the RIDGEPLOT option plots the ridge estimates against the ridge values k; see the description of the RIDGEPLOT option in the section "Dictionary of PLOT Statement Options" for more details. The CONF option plots % confidence intervals for the mean while the PRED option plots % prediction intervals; see the description of these options in the section "Dictionary of PLOT Statement Options" for more details.
If a SELECTION= method is requested, the fitted model equation and the statistics displayed in the margin correspond to the selected model. For the ADJRSQ and CP methods, the selected model is treated as a submodel of the full model. If a CP.*NP. plot is requested, the CHOCKING= and CMALLOWS= options display model selection reference lines; see the descriptions of these options in the section "Dictionary of PLOT Statement Options" and Traditional Graphics for Variable Selection for more details.
The following table lists the keywords available as PLOT statement xvariables and yvariables. All keywords have a trailing dot; for example, "COOKD." requests Cook’s statistic. Neither the OUTPUT statement nor the OUTEST= option needs to be specified.
Keyword 
Description 

Diagnostic Statistics 

COOKD. 
Cook’s influence statistics 
COVRATIO. 
standard influence of observation on covariance of betas 
DFFITS. 
standard influence of observation on predicted value 
H. 
leverage 
LCL. 
lower bound of % confidence interval for individual 
LCLM. 
lower bound of % confidence interval for the mean of 
PREDICTED. 
predicted values 
PRESS. 
residuals from refitting the model with current observation deleted 
RESIDUAL.  R. 
residuals 
RSTUDENT. 
studentized residuals with the current observation deleted 
STDI. 
standard error of the individual predicted value 
STDP. 
standard error of the mean predicted value 
STDR. 
standard error of the residual 
STUDENT. 
residuals divided by their standard errors 
UCL. 
upper bound of % confidence interval for individual 
UCLM. 
upper bound of % confidence interval for the mean of 
Other Keywords Used with Diagnostic Statistics 

NPP. 
normal probabilityprobability plot 
NQQ. 
normal quantilequantile plot 
OBS. 
observation number (cannot plot against OUTEST= statistics) 
Model Fit Summary Statistics 

ADJRSQ. 
adjusted Rsquare 
AIC. 
Akaike’s information criterion 
BIC. 
Sawa’s Bayesian information criterion 
CP. 
Mallows’ statistic 
EDF. 
error degrees of freedom 
GMSEP. 
estimated MSE of prediction, assuming multivariate normality 
IN. 
number of regressors in the model not including the intercept 
JP. 
final prediction error 
MSE. 
mean squared error 
NP. 
number of parameters in the model (including the intercept) 
PC. 
Amemiya’s prediction criterion 
RMSE. 
root MSE 
RSQ. 
Rsquare 
SBC. 
SBC statistic 
SP. 
SP statistic 
SSE. 
error sum of squares 
The following table lists the PLOT statement options by function. These options are available unless the LINEPRINTER option is specified in the PROC REG statement. For complete descriptions, see the section "Dictionary of PLOT Statement Options".
Option 
Description 

General Graphics Options 

ANNOTATE= 
specifies the annotate data set 
CHOCKING=color 
requests a reference line for model selection criteria 
CMALLOWS=color 
requests a reference line for the model selection criterion 
CONF 
requests plots of % confidence intervals for the mean 
DESCRIPTION= 
specifies a description for graphics catalog member 
NAME=’string’ 
names the plot in the graphics catalog 
OVERLAY 
overlays plots from the same model 
PRED 
requests plots of % prediction intervals for individual 
RIDGEPLOT 
requests the ridge trace for ridge regression 
Axis and Legend Options 

LEGEND=LEGENDn 
specifies LEGEND statement to be used 
HAXIS=values 
specifies tick mark values for horizontal axis 
VAXIS=values 
specifies tick mark values for vertical axis 
Reference Line Options 

HREF=values 
specifies reference lines perpendicular to horizontal axis 
LHREF=linetype 
specifies line style for HREF= lines 
LLINE=linetype 
specifies line style for lines displayed by default 
LVREF=linetype 
specifies line style for VREF= lines 
NOLINE 
suppresses display of any default reference line 
VREF=values 
specifies reference lines perpendicular to vertical axis 
Color Options 

CAXIS=color 
specifies color for axis line and tick marks 
CFRAME=color 
specifies color for frame 
CHREF=color 
specifies color for HREF= lines 
CLINE=color 
specifies color for lines displayed by default 
CTEXT=color 
specifies color for text 
CVREF=color 
specifies color for VREF= lines 
Options for Displaying the Fitted Model Equation 

MODELFONT=font 
specifies font of model equation and model label 
MODELHT=value 
specifies text height of model equation and model label 
MODELLAB=’label’ 
specifies model label 
NOMODEL 
suppresses display of the fitted model and the label 
Options for Displaying Statistics in the Plot Margin 

AIC 
displays Akaike’s information criterion 
BIC 
displays Sawa’s Bayesian information criterion 
CP 
displays Mallows’ statistic 
EDF 
displays the error degrees of freedom 
GMSEP 
displays the estimated MSE of prediction assuming 
IN 
displays the number of regressors in the model not including 
JP 
displays the statistic 
MSE 
displays the mean squared error 
NOSTAT 
suppresses display of the default statistics: the number of 
NP 
displays the number of parameters in the model including the 
PC 
displays the PC statistic 
SBC 
displays the SBC statistic 
SP 
displays the statistic 
SSE 
displays the error sum of squares 
STATFONT=font 
specifies font of text displayed in the margin 
STATHT=value 
specifies height of text displayed in the margin 
The following entries describe the PLOT statement options in detail. Note that these options are available unless you specify the LINEPRINTER option in the PROC REG statement.
specifies an input data set that contains appropriate variables for annotation. This applies only to displays created with the current PLOT statement. Refer to SAS/GRAPH Software: Reference for more information.
displays Sawa’s Bayesian information criterion in the plot margin.
specifies the color for filling the area enclosed by the axes and the frame.
requests reference lines corresponding to the equations and , where is the number of parameters in the full model (excluding the intercept) and is the number of parameters in the subset model (including the intercept). The color must be specified; the line is solid and the line is dashed. Only PLOT statements of the form PLOT CP.*NP. produce these lines.
For the purpose of parameter estimation, Hocking (1976) suggests selecting a model where . For the purpose of prediction, Hocking suggests the criterion . You can request the single reference line with the CMALLOWS= option. If, for example, you specify both CHOCKING=RED and CMALLOWS=BLUE, then the line is red and the line is blue (see Figure 74.45).
specifies the color for lines requested with the HREF= option.
specifies the color for lines displayed by default. See the NOLINE option for details.
requests a reference line, where is the number of parameters (including the intercept) in the subset model. The color must be specified; the line is solid. Only PLOT statements of the form PLOT CP.*NP. produce this line.
Mallows (1973) suggests that all subset models with small and near be considered for further study. See the CHOCKING= option for related modelselection criteria.
is a keyword used as a shorthand option to request plots that include % confidence intervals for the mean response (see Figure 74.44). The ALPHA= option in the PROC REG or MODEL statement selects the significance level , which is 0.05 by default. The CONF option is valid for simple regression models only, and is ignored for plots where confidence intervals are inappropriate. The CONF option replaces the CONF95 option; however, the CONF95 option is still supported when the ALPHA= option is not specified. The OVERLAY option is ignored when the CONF option is specified.
specifies the color for text including tick mark labels, axis labels, the fitted model label and equation, the statistics displayed in the margin, and legends.
specifies the color for lines requested with the VREF= option.
specifies a descriptive string, up to 40 characters, that appears in the description field of the PROC GREPLAY master menu.
displays the estimated mean square error of prediction in the plot margin. Note that the estimate is calculated under the assumption that both independent and dependent variables have a multivariate normal distribution.
specifies where reference lines perpendicular to the horizontal axis are to appear.
displays the number of regressors in the model (not including the intercept) in the plot margin.
specifies the LEGEND statement to be used. The LEGEND statement is a global graphics statement; refer to SAS/GRAPH Software: Reference for more information.
specifies the line style for lines requested with the HREF= option. The default linetype is 2. Note that LHREF=1 requests a solid line. Refer to SAS/GRAPH Software: Reference for a table of available line types.
specifies the line style for reference lines displayed by default; see the NOLINE option for details. The default linetype is 2. Note that LLINE=1 requests a solid line.
specifies the line style for lines requested with the VREF= option. The default linetype is 2. Note that LVREF=1 requests a solid line.
specifies the font used for displaying the fitted model label and the fitted model equation. Refer to SAS/GRAPH Software: Reference for tables of software fonts.
specifies the text height for the fitted model label and the fitted model equation.
specifies the label to be displayed with the fitted model equation. By default, no label is displayed. If the label does not fit on one line, it is not displayed. See the section Traditional Graphics for more information.
specifies a descriptive string, up to eight characters, that appears in the name field of the PROC GREPLAY master menu. The default string is REG.
suppresses the display of default reference lines. A default reference line at zero is displayed if residuals are plotted. If the dependent variable is plotted against the independent variable in a simple regression model, then the fitted regression line is displayed by default. Default reference lines are not displayed if the OVERLAY option is specified.
suppresses the display of statistics in the plot margin. By default, the number of observations, Rsquare, adjusted Rsquare, and root MSE are displayed.
displays the number of regressors in the model including the intercept, if any, in the plot margin.
overlays all plots specified in the PLOT statement from the same model on one set of axes. The variables for the first plot label the axes. The procedure automatically scales the axes to fit all of the variables unless the HAXIS= or VAXIS= option is used. Default reference lines are not displayed. A default legend is produced; the LEGEND= option can be used to customize the legend.
is a keyword used as a shorthand option to request plots that include % prediction intervals for individual responses (see Figure 74.44). The ALPHA= option in the PROC REG or MODEL statement selects the significance level , which is 0.05 by default. The PRED option is valid for simple regression models only, and is ignored for plots where prediction intervals are inappropriate. The PRED option replaces the PRED95 option; however, the PRED95 option is still supported when the ALPHA= option is not specified. The OVERLAY option is ignored when the PRED option is specified.
creates overlaid plots of ridge estimates against ridge values for each coefficient. The points corresponding to the estimates of each coefficient in the plot are connected by lines. For ridge estimates to be computed and plotted, the OUTEST= option must be specified in the PROC REG statement, and the RIDGE=list must be specified in either the PROC REG or MODEL statement.
specifies the font used for displaying the statistics that appear in the plot margin. Refer to SAS/GRAPH Software: Reference for tables of software fonts.
specifies the text height of the statistics that appear in the plot margin.
specifies that predicted values at data points with missing dependent variable(s) be included on appropriate plots. By default, only points used in constructing the SSCP matrix appear on plots.
specifies where reference lines perpendicular to the vertical axis are to appear.
Line printer plots are requested with the LINEPRINTER option in the PROC REG statement. Points in line printer plots can be marked with symbols, which can be specified as a single character enclosed in quotes or the name of any variable in the input data set.
If a character variable is used for the symbol, the first (leftmost) nonblank character in the formatted value of the variable is used as the plotting symbol. If a character in quotes is specified, that character becomes the plotting symbol. If a character is used as the plotting symbol, and if there are different plotting symbols needed at the same point, the symbol ’?’ is used at that point.
If an unformatted numeric variable is used for the symbol, the symbols ’1’, ’2’, ..., ’9’ are used for variable values 1, 2, ..., 9. For noninteger values, only the integer portion is used as the plotting symbol. For values of 10 or greater, the symbol ’*’ is used. For negative values, a ’?’ is used. If a numeric variable is used, and if there is more than one plotting symbol needed at the same point, the sum of the variable values is used at that point. If the sum exceeds 9, the symbol ’*’ is used.
If a symbol is not specified, the number of replicates at the point is displayed. The symbol ’*’ is used if there are 10 or more replicates.
If the LINEPRINTER option is used, you can specify the following options in the PLOT statement after a slash (/):
clears any collected scatter plots before plotting begins but does not turn off the COLLECT option. Use this option when you want to begin a new collection with the plots in the current PLOT statement. For more information about collecting plots, see the COLLECT and NOCOLLECT options in this section.
specifies that plots begin to be collected from one PLOT statement to the next and that subsequent plots show an overlay of all collected plots. This option enables you to overlay plots before and after changes to the model or to the data used to fit the model. Plots collected before changes are unaffected by the changes and can be overlaid on later plots. You can request more than one plot with this option, and you do not need to request the same number of plots in subsequent PLOT statements. If you specify an unequal number of plots, plots in corresponding positions are overlaid. For example, the statements
plot residual.*predicted. y*x / collect; run;
produce two plots. If these statements are then followed by
plot residual.*x; run;
two plots are again produced. The first plot shows residual against X values overlaid on residual against predicted values. The second plot is the same as that produced by the first PLOT statement.
Axes are scaled for the first plot or plots collected. The axes are not rescaled as more plots are collected.
Once specified, the COLLECT option remains in effect until the NOCOLLECT option is specified.
sets the number of scatter plots that can be displayed across the page. The procedure begins with one plot per page. The value of the HPLOTS= option remains in effect until you change it in a later PLOT statement. See the VPLOTS= option for an example.
specifies that the collection of scatter plots ends after adding the plots in the current PLOT statement. PROC REG starts with the NOCOLLECT option in effect. After you specify the NOCOLLECT option, any following PLOT statement produces a new plot that contains only the plots requested by that PLOT statement.
For more information, see the COLLECT option.
enables requested scatter plots to be superimposed. The axes are scaled so that points on all plots are shown. If the HPLOTS= or VPLOTS= option is set to more than one, the overlaid plot occupies the first position on the page. The OVERLAY option is similar to the COLLECT option in that both options produce superimposed plots. However, OVERLAY superimposes only the plots in the associated PLOT statement; COLLECT superimposes plots across PLOT statements. The OVERLAY option can be used when the COLLECT option is in effect.
changes the default plotting symbol used for all scatter plots produced in the current and in subsequent PLOT statements. Both SYMBOL=” and SYMBOL=’ ’ are allowed.
If the SYMBOL= option has not been specified, the default symbol is ’1’ for positions with one observation, ’2’ for positions with two observations, and so on. For positions with more than 9 observations, ’*’ is used. The SYMBOL= option (or a plotting symbol) is needed to avoid any confusion caused by this default convention. Specifying a particular symbol is especially important when either the OVERLAY or COLLECT option is being used.
If you specify the SYMBOL= option and use a number for character, that number is used for all points in the plot. For example, the statement
plot y*x / symbol='1';
produces a plot with the symbol ’1’ used for all points.
If you specify a plotting symbol and the SYMBOL= option, the plotting symbol overrides the SYMBOL= option. For example, in the statements
plot y*x y*v='.' / symbol='*';
the symbol used for the plot of Y against X is ’*’, and a ’.’ is used for the plot of Y against V.
If a paint symbol is defined with a PAINT statement, the paint symbol takes precedence over both the SYMBOL= option and the default plotting symbol for the PLOT statement.
sets the number of scatter plots that can be displayed down the page. The procedure begins with one plot per page. The value of the VPLOTS= option remains in effect until you change it in a later PLOT statement.
For example, to specify a total of six plots per page, with two rows of three plots, use the HPLOTS= and VPLOTS= options as follows:
plot y1*x1 y1*x2 y1*x3 y2*x1 y2*x2 y2*x3 / hplots=3 vplots=2; run;
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