What is the "Use True 3-P MLE on Weibull" option on the Calculations page of the User Setup in Weibull++?
This option simply indicates how the parameters of the 3-parameter Weibull distribution are to be estimated when using maximum likelihood estimation (MLE). If this option is not selected, Weibull++ first determines the estimate of the location parameter by nonlinear regression. Once this estimate has been determined, Weibull++ uses MLE to estimate beta and eta. This methodology is generally more appropriate for the analysis of life data.
If this option is selected, then all three parameters are estimated simultaneously using MLE. However, a pure MLE solution on a 3-parameter Weibull distribution is problematic in certain regions of beta and may yield results that do not make sense in the context of life data analysis (e.g. very large negative values for gamma, etc.).
Why is rank regression not available as an analysis method in ALTA?
Although rank regression (graphical methods) is fairly simple, it is quite laborious. Furthermore, many issues surrounding its use require careful consideration. Some of these issues are presented next:
Copyright 2003 ReliaSoft Corporation, ALL RIGHTS RESERVED