The RELIABILITY Procedure 
PROBPLOT Statement 
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.
represents the data for which a probability plot is to be produced. The variable must be a numeric variable in the input data set.
indicates which observations in the input data set are right censored. You specify the values of censorvariable that represent censored observations by placing those values in parentheses after the variable name. If your data are not right censored, then you can omit the specification of censorvariable; otherwise, censorvariable must be a numeric variable in the input data set.
is another method of specifying the data for which a probability plot is to be produced. You can use this syntax in a situation where uncensored, intervalcensored, leftcensored, and rightcensored values occur in the same set of data. Table 12.26 shows how you use this syntax to specify different types of censoring by using combinations of missing and nonmissing values. See the section Lognormal Analysis with Arbitrary Censoring for an example that uses this syntax to create a probability plot.
are one or two group variables. If no group variables are specified, a single probability plot is produced. The groupvariables can be numeric or character variables in the input data set.
Note that the parentheses surrounding the groupvariables are needed only if two group variables are specified.
control the features of the probability plot. All options are specified after the slash (/) in the PROBPLOT statement. See the section Summary of Options, which follows, for a list of all options by function.
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 parameter correlation matrix 
COVB 
requests parameter covariance matrix 
FITTYPE  FIT= 
specifies method of estimating distribution parameters 
LSYX 
least squares fit to the probability plot. The probability axis is the dependent variable. 
 LSXY 
least squares fit to the probability plot. The lifetime axis is the dependent variable. 
 MLE 
maximum likelihood (default) 
 MODEL 
use the fit from the preceding MODEL statement 
 NONE 
no fit is computed 
 WEIBAYES 
Weibayes method 
<(CONFIDENCECONF=number)> 
number is the confidence coefficient for the Weibayes fit and is between 0 and 1. The default value is 0.95. 
ITPRINT 
requests iteration history for maximum likelihood fit 
ITPRINTEM 
requests iteration history for the Turnbull algorithm 
LRCL 
requests likelihood ratio confidence intervals for distribution parameters 
LRCLPER 
requests likelihood ratio confidence intervals for distribution percentiles 
LOCATION=number <LINIT> 
specifies fixed or initial value of location parameter 
MAXIT=number 
specifies maximum number of iterations allowed for maximum likelihood fit 
MAXITEM=number1 <,number2> 
number1 specifies maximum number of iterations allowed for Turnbull algorithm. Iteration history will be printed in increments of number2 if requested with ITPRINTEM. See the section IntervalCensored Data for details. 
NOPCTILES 
suppresses computation of percentiles for standard list of percentage points 
NOPOLISH 
suppress setting small interval probabilities to zero in the Turnbull algorithm. See the section IntervalCensored Data for details. 
NPINTERVALS= 
specifies type of nonparametric confidence interval displayed in a probability plot 
POINTWISE  POINT 
pointwise confidence intervals for the CDF 
 SIMULTANEOUS 

 SIMUL<number1, number2> 
simultaneous confidence intervals for the CDF. See the section Simultaneous Confidence Intervals for details. 
PCTLIST=numberlist 
specifies 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. 
type of parametric pointwise confidence interval displayed in a probability plot. The default type is PROBABILITY, pointwise confidence intervals on cumulative failure probability. 

LIKELIHOOD  LRCI 
likelihood ratio confidence intervals 
 PERCENTILES  PER 
pointwise parametric confidence intervals for the percentiles of the fitted CDF 
 PROBABILITY  CDF 
pointwise parametric confidence intervals for the cumulative failure probabilities. See the section Reliability Function for details. 
PPOS= 
specifies plotting position type. See the section Probability Plotting for details. 
EXPRANK 
expected ranks 
 MEDRANK 
median ranks 
 MEDRANK1 
median ranks (exact formula) 
 KM 
KaplanMeier 
 MKM 
modified KaplanMeier (default) 
(NA  NELSONAALEN) 
 NelsonAalen 
PPOUT 
request table of cumulative probabilities 
PRINTPROBS 
print intervals and associated probabilities for the Turnbull algorithm 
PROBLIST=numberlist 
specifies list of initial values for Turnbull algorithm. See the section IntervalCensored Data for details. 
PSTABLE=number 
specifies stable parameterization. The number must be between zero and one. See the section Stable Parameters for further information. 
READOUT 
analyzes data with readout structure 
SCALE=number <SCINIT> 
specifies fixed or initial value of scale parameter 
SHAPE=number <SHINIT> 
specifies fixed or initial value of shape parameter 
SINGULAR=number 
specifies singularity criterion for matrix inversion 
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 12.49 for the distributions with a threshold parameter. 
TOLLIKE=number 
specifies criterion for convergence in the Turnbull algorithm. Default is . See the section IntervalCensored Data for details. 
TOLPROB=number 
specifies criterion for setting interval probability to zero in the Turnbull algorithm. Default is . See the section IntervalCensored Data for details. 
Table 12.30 lists plot layout options available when you use traditional graphics.
Option 
Option Description 

CENBIN 
plots censored data as frequency counts rather than as individual points 
CENSYMBOL= 

symbol  (symbol list) 
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 for failures. 
HOFFSET=value 
specifies offset for horizontal axis 
INBORDER 
requests a border around probability plots 
INTERTILE=value 
specifies distance between tiles 
LFIT=linetype  (linetype list)) 
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, and can be separated by blanks or commas or can be a list in the form to <by >. 
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= 
specifies number of columns plotted on a page 
NOCENPLOT 
suppresses plotting of censored data points 
NOCONF 
suppresses plotting of percentile confidence curves 
NOFIT 
suppresses plotting of fit line and percentile confidence curves 
NOFRAME 
suppresses frame around plotting area 
NOINSET 
suppresses inset 
NOPPLEGEND 
suppresses legend for overlaid probability plots 
NOPPOS 
suppresses plotting of symbols for failures in a probability plot 
NROWS= 
specifies number of rows plotted on a page 
ORDER1=DATA  FORMATTED  
specifies display order for values of the first GROUP= variable 
ORDER2=DATA  FORMATTED  
specifies 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 legend for overlaid probability plots 
PPOSSYMBOL=symbol  (symbol list) 
symbols representing failures on a probability plot 
ROTATE 
requests probability plots with probability scale on horizontal axis 
SHOWMULTIPLES 
display the count for multiple overlaying symbols 
TURNVLABELS 
vertically strings out characters in labels for vertical axis 
VOFFSET=value 
length of offset at upper end of vertical axis 
WFIT=linetype 
line width for fit line and confidence curves 
Table 12.31 lists plot layout options available when you use 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= 
specifies number of columns plotted on a page 
NOCENPLOT 
suppresses plotting of censored data points 
NOCONF 
suppresses plotting of percentile confidence curves 
NOFIT 
suppresses plotting of fit line and percentile confidence curves 
NOINSET 
suppresses inset 
NOPPLEGEND 
suppresses legend for overlaid probability plots 
NOPPOS 
suppresses plotting of symbols for failures in a probability plot 
NROWS= 
specifies number of rows plotted on a page 
ORDER1=DATA  FORMATTED  
specifies display order for values of the first GROUP= variable 
ORDER2=DATA  FORMATTED  
specifies 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 probability scale on horizontal axis 
Table 12.32 lists reference line options available when you use 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= 
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 line style for HREF= lines 

LVREF=linetype 
specifies 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= 
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 12.33 lists reference line options available when you use 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 
The following options control the appearance of the text when you use traditional graphics. These options are not available if ODS Graphics is enabled.
Option 
Option Description 

FONT=font 
specifies a software font for text 
HEIGHT=value 
specifies height of text used outside framed areas 
INFONT=font 
specifies a software font for text inside framed areas 
INHEIGHT=value 
specifies height of text inside framed areas 
Table 12.35 lists options to control the appearance of the axes when you use 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= 
specifies the line thickness for axes and frame 
Table 12.36 lists options to control the appearance of the axes when you use ODS graphics.
Option 
Option Description 

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 
The following options control colors and patterns used in the graph when you use traditional graphics. These options are not available if ODS Graphics is enabled.
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 representing failures on a probability plot 
The following options 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.
Option 
Option Description 

DESCRIPTION=‘string’ 
description for graphics catalog member 
NAME=‘string’ 
name for plot in graphics catalog 
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