Weibull Probability Paper - Advanced Tab

Select the Advanced tab of the Weibull Probability Paper dialog box to access options to produce a customized Weibull probability plot; when no data are plotted but only the probability scale and the logarithmic scale for failure times is shown, such plots are also called probability paper.

The default location (offset) parameter is equal to 0 (zero); however, if you have previously fitted the Weibull distribution to a variable (see the Weibull Analysis: Results (Raw Data) dialog box topic), the respective location parameter value is "remembered."

Probability plot (paper)

Click this button to produce the Weibull probability paper plot. See the Introductory Overview for details concerning how this plot is constructed, and how it is useful for fitting the Weibull distribution to observed failure time data.

For a description of how nonparametric estimates of the cumulative distribution function are computed for complete, single censored, and multiple censored data see: Failure order for single or uncensored data and Modified failure order for multiple-censored data.

Options for Weibull probability paper

Use the options in this group box to control the scaling of the axes in the Weibull probability plot.

Min. p, Max. p, Step size.

p, Step size. Enter the values to be used for the scaling of the probability axis in the Weibull paper in these boxes.

Offset (location, min t)

Enter the value that will be interpreted as the location parameter for the Weibull distribution (or adjust the value using the microscrolls). If a Weibull distribution has been fit to raw data previously, then this parameter is "remembered" from the previous analysis. The horizontal x-axis in the Weibull paper will be scaled such that the x-axis metric will represent the natural logarithm of the respective failure times minus the location parameter (the x-axis labeling will of course reflect the desired actual range, i.e., the minimum and maximum failure times).

Max. time to failure.

Enter the value to be used to scale the x-axis (or adjust the value using the microscrolls). Note that Statistica will not use this value exactly; instead this value will be approximated, and "neat" (round) scale values will always be used for the x-axis scaling (the Max. time to failure value will always be less than or equal to the actual maximum value used on the x-axis, i.e., it is guaranteed to be included in the range represented by the x-axis).

Step size for t

Enter the value to be used for the step-size of the x-axis values (or adjust the value using the microscrolls).

Add p labels and grid lines at extreme ends

Select this check box if you want Statistica to add grid lines and scale labels for the probability scale (on the left y-axis) for the extreme ends of the normal distribution. For example, if you request as the Min. p and Max. p values .1 and .9, respectively, and .1 as the step size, Statistica will place grid lines and left y-axis scale labels at .1, .2, ..., .90. The program will also add grid lines and labels at .01, .05, .95, .99, and .999.

Add principal abscissa (characteristic life)

Select this check box if you want Statistica to display a horizontal line in the plot indicating the characteristic life (the characteristic life is defined as the point in time where 63.2 percent of the population will have failed; this point is also equal to the respective scale parameter b of the two-parameter Weibull distribution with θ = 0; otherwise it is equal to b+θ).