<label:>PROBPLOT
variable <
censorvariable(values)> <=groupvariables> </ options> ;
<label:>PROBPLOT
(variable1 variable2) <=groupvariables> </ options> ;
You use the PROBPLOT statement to create a probability plot from complete, leftcensored, rightcensored, or intervalcensored data.
You can specify the keyword PPLOT as an alias for PROBPLOT. You can specify any number of PROBPLOT statements after a PROC RELIABILITY statement. Each PROBPLOT statement creates a probability plot and an associated analysis. The probability distribution used in creating the probability plot and performing the analysis is determined by the DISTRIBUTION statement. You can specify an optional label to distinguish between multiple PROBPLOT statements in the output.
See the section Analysis of RightCensored Data from a Single Population and the section Weibull Analysis Comparing Groups of Data for examples that create probability plots with the PROBPLOT statement.
To create a probability plot, you must specify one variable. If your data are right censored, you must specify a censorvariable and, in parentheses, the values of the censorvariable that correspond to censored data values.
You can optionally specify one or two groupvariables (also referred to as classification variables). The PROBPLOT statement displays a probability plot for each level of the groupvariables. The observations in a given level are called a cell.
The elements of the PROBPLOT statement are described as follows.
Table 16.35 lists analysis options that are available when you use either traditional graphics or ODS Graphics.
Table 16.35: Analysis Options
Option 
Option Description 


CONFIDENCE=number 
Specifies the confidence coefficient for all confidence intervals. The number must be between 0 and 1. The default value is 0.95 

CONVERGE=number 
Specifies the convergence criterion for maximum likelihood fit. See the section Maximum Likelihood Estimation for details. 

CONVH=number 
Specifies the convergence criterion for the relative Hessian convergence criterion. See the section Maximum Likelihood Estimation for details. 

CORRB 
Requests the parameter correlation matrix. 

COVB 
Requests the parameter covariance matrix. 

FITTYPE  FIT= fitspecification 
Specifies the method of estimating distribution parameters. The available fitspecifications and their meanings are shown in the following table. 



INEST  IN=SASdataset 
Specifies a SAS data set that can contain initial values, equality constraints, upper bounds, or lower bounds for the scale, shape, and threshold parameters in a threeparameter Weibull model for lifetime data, and applies only to threeparameter Weibull models. See the section INEST Data Set for the ThreeParameter Weibull for details. 

ITPRINT 
Requests the iteration history for maximum likelihood fit. 

ITPRINTEM 
Requests the iteration history for the Turnbull algorithm. 

LRCL 
Requests likelihood ratio confidence intervals for distribution parameters. 

LRCLPER 
Requests likelihood ratio confidence intervals for distribution percentiles. 

LRCLSURV 
Requests likelihood ratio confidence intervals for survival and cumulative distribution functions at times specified with the SURVTIME=numberlist option. 

LOCATION=number <LINIT> 
Specifies a fixed or initial value of location parameter. 

MAXIT=number 
Specifies the maximum number of iterations allowed for a maximum likelihood fit. 

MAXITEM=number1 <,number2> 
number1 Specifies the maximum number of iterations allowed for the Turnbull algorithm. Iteration history will be printed in increments of number2 if an iteration history is requested with ITPRINTEM. See the section IntervalCensored Data for details. 

NOPCTILES 
Suppresses computation of percentiles for standard list of percentage points. 

NOPOLISH 
Suppresses the setting of small interval probabilities to 0 in the Turnbull algorithm. See the section IntervalCensored Data for details. 

NPINTERVALS=intervaltype 
Specifies the type of nonparametric confidence interval displayed in a probability plot. The available types of intervals are listed in the following table. 



PCTLIST=numberlist 
Specifies a list of percentages for which to compute percentile estimates. The numberlist must be a list of numbers separated by blanks or commas. Each number in the list must be between 0 and 100. If this option is not specified, percentiles are computed for a standard list of percentages. 

PINTERVALS=intervaltype 
Specifies the type of parametric pointwise confidence interval displayed in a probability plot. The available types of intervals are listed in the following table. The default type is PROBABILITY, pointwise confidence intervals on cumulative failure probability. 



PPOS=plottingposition 
Specifies the plottingposition type used to compute nonparametric estimates of the probability distribution function. See the section Probability Plotting for details. The plotting position types available are shown in the following table. 



PPOUT 
Requests a table of nonparametric cumulative probabilities in the printed output. 

PRINTPROBS 
Specifies that intervals and associated probabilities for the Turnbull algorithm be printed. 

PROBLIST=numberlist 
Specifies a list of initial values for Turnbull algorithm. See the section IntervalCensored Data for details. 

PSTABLE=number 
Specifies a stable parameterization. The number must be between 0 and 1. See the section Stable Parameters for further information. 

READOUT 
Specifies the data have the readout structure. 

SCALE=number <SCINIT> 
Specifies a fixed or initial value of the scale parameter. 

SHAPE=number <SHINIT> 
Specifies a fixed or initial value of the shape parameter. 

SINGULAR=number 
Specifies the singularity criterion for matrix inversion. 

SURVTIME=numberlist 
Requests that the survival function, cumulative distribution function, and confidence limits be computed for values in numberlist. See the section Reliability Function for details. 

THRESHOLD=number 
Specifies a fixed threshold parameter. See Table 16.57 for the distributions with a threshold parameter. 

TOLLIKE=number 
Specifies the criterion for convergence in the Turnbull algorithm. The default is . See the section IntervalCensored Data for details. 

TOLPROB=number 
Specifies the criterion for setting interval probabilities to 0 in the Turnbull algorithm. The default is . See the section IntervalCensored Data for details. 
Table 16.36 lists analysis options that are available when ODS Graphics is enabled.
Table 16.36: Analysis Options for ODS Graphics
Option 
Option Description 


PROFILE<(options)> 
Requests a profile loglikelihood plot of the threshold parameter for a threeparameter Weibull distribution. The options listed in the following table are available; they are specified by enclosing them in parentheses after the PROFILE option. 


Table 16.37 lists plot layout options that are available when you use traditional graphics.
Table 16.37: Probability Plot Layout Options for Traditional Graphics
Option 
Option Description 

CENBIN 
Specifies that censored data be plotted as frequency counts rather than as individual points. 
CENSYMBOL= 

symbol  (symbollist) 
Specifies symbols for censored values. The symbol is one of the symbol names (plus, star, square, diamond, triangle, hash, paw, point, dot, circle) or a letter (A–Z). For overlaid plots for groups of data, you can specify different symbols for the groups with a list of symbols or letters, separated by blanks, enclosed in parentheses. If no CENSYMBOL option is specified, the symbol used for censored values is the same as the symbol used for failures. 
HOFFSET=value 
Specifies the offset for the horizontal axis. 
INBORDER 
Requests a border around probability plots. 
INTERTILE=value 
Specifies the distance between tiles. 
LFIT=linetype  (linetype list)) 
Specifies line styles for fit lines and confidence curves in a probability plot. The linetype list is a list of numbers from 1 to 46 representing different linetypes; they can be separated by blanks or commas or can be a list in the form to <by >. 
MISSING1 
Requests that missing values of the first GROUP= variable be treated as a level of the variable. 
MISSING2 
Requests that missing values of the second GROUP= variable be treated as a level of the variable. 
NCOLS=n 
Specifies that n columns be plotted on a page. 
NOCENPLOT 
Suppresses the plotting of censored data points. 
NOCONF 
Suppresses the plotting of percentile confidence curves. 
NOFIT 
Suppresses the plotting of fit line and percentile confidence curves. 
NOFRAME 
Suppresses the frame around the plotting area. 
NOINSET 
Suppresses the inset. 
NOPPLEGEND 
Suppresses the legend for overlaid probability plots 
NOPPOS 
Suppresses plotting of symbols for failures in a probability plot. 
NROWS=n 
Specifies that n rows be plotted on a page. 
ORDER1=DATA  FORMATTED  
Specifies display order for values of the first GROUP= variable. 
ORDER2=DATA  FORMATTED  
Specifies the display order for values of the second GROUP= variable. 
OVERLAY 
Requests overlaid plots for group variables. 
PCONFPLT 
Plots confidence intervals on probabilities for readout data. 
PPLEGEND = legendstatementname 

 NONE 
Identifies LEGENDn statement to specify a legend for overlaid probability plots. 
PPOSSYMBOL=symbol  (symbollist) 
Specifies symbols to represent failures on a probability plot. 
ROTATE 
Requests probability plots with the probability scale on the horizontal axis. 
SHOWMULTIPLES 
Requests that the count be displayed for multiple overlaying symbols. 
TURNVLABELS 
Vertically strings out characters in labels for the vertical axis. 
VOFFSET=value 
Specifies value as the length of the offset at the upper end of the vertical axis. 
WFIT=n 
Specifies the line width for the fit line and confidence curves. 
Table 16.38 lists plot layout options that are available when you use ODS graphics.
Table 16.38: Probability Plot Layout Options for ODS Graphics
Option 
Option Description 

MISSING1 
Requests that missing values of first GROUP= variable be treated as a level of the variable. 
MISSING2 
Requests that missing values of second GROUP= variable be treated as a level of the variable. 
NCOLS=n 
Specifies that n columns be plotted on a page. 
NOCENPLOT 
Suppresses plotting of censored data points. 
NOCONF 
Suppresses plotting of percentile confidence curves. 
NOFIT 
Suppresses plotting of the fit line and percentile confidence curves. 
NOINSET 
Suppresses the inset. 
NOPPLEGEND 
Suppresses the legend for overlaid probability plots. 
NOPPOS 
Suppresses plotting of symbols for failures in a probability plot. 
NROWS=n 
Specifies that n rows be plotted on a page. 
ORDER1=DATA  FORMATTED  

FREQ  INTERNAL 
Specifies the display order for values of the first GROUP= variable. 
ORDER2=DATA  FORMATTED  

FREQ  INTERNAL 
Specifies the display order for values of the second GROUP= variable. 
OVERLAY 
Requests overlaid plots for group variables. 
PCONFPLT 
Plots confidence intervals on probabilities for readout data. 
ROTATE 
Requests probability plots with the probability scale on the horizontal axis. 
Table 16.39 lists reference line options that are available when you use traditional graphics.
Table 16.39: Reference Line Options for Traditional Graphics
Option 
Option Description 


HREF <(INTERSECT)>=valuelist 
Requests reference lines perpendicular to 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. 

HREFLABELS=(’label1’ …’labeln’) 
Specifies labels for HREF= lines. 

HREFLABPOS=n 
Specifies vertical position of labels for HREF= lines. The valid values for n and the corresponding label placements are shown in the following table:


LHREF=linetype 
Specifies the line style for HREF= lines. 

LVREF=linetype 
Specifies the line style for VREF= lines. 

VREF <(INTERSECT)>=valuelist 
Specifies reference lines perpendicular to 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. 

VREFLABELS=(’label1’ …’labeln’) 
Specifies labels for VREF= lines. 

VREFLABPOS=n 
Specifies horizontal position of labels for VREF= lines. The valid values for n and the corresponding label placements are shown in the following table:

Table 16.40 lists reference line options that are available when you use ODS graphics.
Table 16.40: Reference Line Options for ODS Graphics
Option 
Option Description 

HREF  

LREF <(INTERSECT)>=valuelist 
Requests reference lines perpendicular to 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. 
HREFLABELS  

LREFLABELS =(’label1’ …’labeln’) 
Specifies labels for HREF= lines. 
VREF  

PREF <(INTERSECT)>=valuelist 
Specifies reference lines perpendicular to 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. 
VREFLABELS  

PREFLABELS=(’label1’ …’labeln’) 
Specifies labels for VREF= lines. 
Table 16.41 lists options that control the appearance of the text when you use traditional graphics. These options are not available if ODS Graphics is enabled.
Table 16.41: Text Enhancement Options
Option 
Option Description 

FONT=font 
Specifies a software font for text. 
HEIGHT=value 
Specifies the height of text used outside framed areas. 
INFONT=font 
Specifies a software font for text inside framed areas. 
INHEIGHT=value 
Specifies the height of text inside framed areas. 
Table 16.42 lists options that control the appearance of the axes when you use traditional graphics.
Table 16.42: Axis Options for Traditional Graphics
Option 
Option Description 

LAXIS=value1 to value2<by value3> 
Specifies tick mark values for the lifetime 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. This method of specification of tick marks is not valid for logarithmic axes. Examples of LAXIS= lists are laxis = 1 to 10 laxis = 0 to 200 by 10 
LGRID=number 
Specifies a line style for all grid lines. The number is between 1 and 46 and specifies a linestyle for grids. 
LIFELOWER  LLOWER=number 
Specifies the lower limit on the lifetime axis scale. The LLOWER option specifies number as the lower lifetime axis tick mark. The tick interval and the upper lifetime axis limit are determined automatically. This option has no effect if the LAXIS option is used. 
LIFEUPPER  LUPPER=number 
Specifies the upper limit on the lifetime axis scale. The LUPPER option specifies number as the upper lifetime axis tick mark. The tick interval and the lower lifetime axis limit are determined automatically. This option has no effect if the LAXIS option is used. 
MPGRID 
Adds a minor grid for the probability axis. 
MINORLOGGRID 
Adds a minor grid for log axes. 
NOGRID 
Suppresses grid lines. 
NOLLABEL 
Suppresses label for life, or analysis variable, axis. 
NOLTICK 
Suppresses tick marks and tick mark labels for lifetime or analysis variable axis. 
NOPLABEL 
Suppresses label for probability axis. 
NOPTICK 
Suppresses tick marks and tick mark labels for the probability axis. 
NTICK=number 
Specifies the number of tick intervals for the lifetime axis. This option has no effect if the LAXIS option is used. 
PCTLOWER  PLOWER=number 
Specifies the lower limit on probability axis scale. 
PCTUPPER  PUPPER=number 
Specifies the upper limit on probability axis scale. 
PAXISLABEL=‘string’ 
Specifies a label for the probability axis. 
WAXIS=n 
Specifies the line thickness for axes and frame. 
Table 16.43 lists options that control the appearance of the axes when you use ODS Graphics.
Table 16.43: Axis Options for ODS Graphics
Option 
Option Description 

LAXIS=value1 to value2<by value3> 
Specifies tick mark values for the lifetime 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. This method of specification of tick marks is not valid for logarithmic axes. Examples of LAXIS= lists are laxis = 1 to 10 laxis = 0 to 200 by 10 
LIFELOWER  LLOWER=number 
Specifies the lower limit on the lifetime axis scale. The LLOWER option specifies number as the lower lifetime axis tick mark. The tick interval and the upper lifetime axis limit are determined automatically. This option has no effect if the LAXIS option is used. 
LIFEUPPER  LUPPER=number 
Specifies the upper limit on the lifetime axis scale. The LUPPER option specifies number as the upper lifetime axis tick mark. The tick interval and the lower lifetime axis limit are determined automatically. This option has no effect if the LAXIS option is used. 
MINORLOGGRID 
Adds a minor grid for log axes. 
NOGRID 
Suppresses grid lines. 
PCTLOWER  PLOWER=number 
Specifies the lower limit on probability axis scale. 
PCTUPPER  PUPPER=number 
Specifies the upper limit on probability axis scale. 
PAXISLABEL=‘string’ 
Specifies a label for the probability axis. 
Table 16.44 lists options that control colors and patterns used in the graph when you use traditional graphics. These options are not available if ODS Graphics is enabled.
Table 16.44: Color and Pattern Options
Option 
Option Description 

CAXIS=color 
Color for axis 
CCENSOR=color 
Color for filling censor plot area 
CENCOLOR=color 
Color for censor symbol 
CFIT=color  (color list) 
color for fit lines and confidence curves in a probability plot 
CFRAME=color 
Color for frame 
CFRAMESIDE=color 
Color for filling frame for row labels 
CFRAMETOP=color 
Color for filling frame for column labels 
CGRID=color 
Color for grid lines 
CHREF=color 
Color for HREF= lines 
CTEXT=color 
Color for text 
CVREF=color 
Color for VREF= lines 
PPOSCOLOR=color  (color list) 
Colors of symbols that represent failures on a probability plot 
Table 16.45 lists options that control the use of a graphics catalog to store graphs if you use traditional graphics. These options are not available if ODS Graphics is enabled.
Table 16.45: Graphics Catalog Options
Option 
Option Description 

DESCRIPTION=‘string’ 
Description for graphics catalog member 
NAME=‘string’ 
Name for plot in graphics catalog 