Weibull Probability Paper

Produces a user-defined Weibull probability plot (with probability scales); 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.

Parameters for Weibull plot (paper)

Element Name Description
Input variables Specifies whether the (optional) input list of dependent continuous variables describes a list of variables with failure times (multiple analyses will be performed, one for each variable), or a list of variables describing the start/stop times for a single measure.

 In the latter case (single measure, single analysis) you must specify for input either two (continuous dependent) variables with start and stop times for each observation (the analysis will be performed on the differences between the two values, i.e., on the elapsed times), or you can select six (continuous dependent) variables containing dates. Specifically, these variables should contain the month (1 to 12), day (1 to 31), and year when the particular observation began (e.g., when a patient was admitted to the hospital), and the month, day, and year when the observation was terminated (due to death/failure or censoring, e.g., when a patient was dismissed from the hospital). While processing the data, Statistica will compute the number of days that elapsed between dates, and perform the analysis on this measure. Note that if the value of the year is less than 100, Statistica will automatically assume that the year refers to the 20th century; for example, the year 88 would be converted into 1988.
Minimum p value Specifies the minimum value of p to be used for the scaling of the probability axis in the Weibull paper.
Maximum p value Specifies the maximum value of p to be used for the scaling of the probability axis in the Weibull paper.
Step size for p Specifies the stepsize (used for scaling of the probability axis) for the Weibull probability plot (paper).
Weibull offset Specifies the value that will be interpreted as the location parameter for the Weibull distribution.
Maximum time to failure Specifies the value to be used to scale the x-axis for the Weibull probability plot (paper).
Step size for time Specifies the value to be used for the step-size of the x-axis values for the Weibull probability plot (paper).

Plots Options

Element Name Description
Add P labels and grid lines Select this option if you want to add grid lines and scale labels for the probability scale (on the left y-axis) for the extreme ends of the normal distribution.
Add characteristic life Select this option if you want to place a horizontal line into the plot indicating the characteristic life. In Weibull and reliability/failure time analysis, 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 q = 0; otherwise it is equal to b+q).
Add constant Add a constant to the data to zero failure times; the Weibull distribution is bounded on the left side; i.e., all values must be greater than the respective location parameter (greater than 0, by default). If the Add constant option is selected, Statistica replaces zero failure times with the constant before fitting or plotting the Weibull distribution.
Value to add The value (constant) to add to 0 failure times. The Weibull distribution is bounded on the left side; i.e., all values must be greater than the respective location parameter (greater than 0, by default). If the add constant is true, then Statistica replaces zero failure times with the constant before fitting or plotting the Weibull distribution.