The Alter Parameters feature is available for both Weibull++ life data folios and ALTA life-stress data folios. It enables you to experiment with possible alternative scenarios by altering the estimated parameters of the fitted model.
After you calculate the parameters for your data set, you can access the tool by choosing [Life Data/Life-Stress Data] > Options > Alter Parameters and then selecting one of the following options:
Alter Parameters (w/o Recalculation) allows you to alter the value of one (or more) parameters, while keeping the original values of the rest of the parameters and the variance/covariance matrix the same.
Alter One Parameter (and Recalculate) allows you to alter one of the parameter values, and then have the software estimate the other parameter values that would result in a good fit for the model. In Weibull++ life data folios, this option is available only for data sets that were analyzed with the MLE analysis method and either the 2P- or 3P-Weibull distribution.
If you wish to modify the value of the gamma parameter of the 3P-Weibull distribution, you must first select the Use true 3-P MLE on Weibull check box in the Calculations page of the Application Setup, and then estimate all three parameters using MLE. Note that the pure MLE solution is not always stable, and may fail for some data sets.
For both options, the LK values, solution line on plots and all subsequent analyses will be based on the modified set of parameters. To go back to the true parameters, click the Calculate icon on the folio's control panel.
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