Alter Parameters

The Alter Parameters feature is available for life data folios, life-stress data folios and reliability growth data folios. It enables you to experiment with possible alternative scenarios by altering the estimated parameters of the fitted model.

Life Data and Life-Stress Data Folios

For life data and life-stress data folios, 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.

Reliability Growth Data (RGA) Folios

For reliability growth data folios, the feature is available for any data set calculated using any model except the Crow Extended and Crow Extended - Continuous Evaluation. Furthermore, for data sets calculated with the Crow-AMSAA (NHPP) model, this functionality is not available for Change of Slope calculations.

This feature assumes that the likelihood function and the Fisher Matrix (evaluated at the original parameter estimates) remain the same. In plots, the position of the data points remain the same but the solution line and all subsequent analyses made via the Quick Calculation Pad and other tools are based on the modified parameter values. Therefore, the analysis may be appropriate only within the context of your specific "what-if" analysis.

To use this feature, choose Growth Data > Options > Alter Parameters or click the icon on the Main page of the control panel.

The Alter Parameters window appears. Type the new value for the parameter(s) you wish to change. The new value of the parameters will appear in the Results area of the growth data folio control panel with the label "User Modified Results"displaying in the analysis settings area, as shown in the following example.