Why doesn the calculated MLE line track the data points on my probability plot in Weibull++?
The reason that the fitted MLE model does not track the data points is due to differences in the way the plot and the MLE model are generated. The probability plot incorporates estimates of the unreliability in order to provide y-axis values to go with the failure times on the x-axis. In Weibull++, these unreliability estimates are provided by median ranks or Kaplan-Meier estimates. The maximum likelihood estimator (MLE) method of parameter estimation only uses the failure and suspension (x-axis) data when generating the unreliability model. Consequently, the fitted model may not necessarily track the data points on the plot. However, this does not mean that the model or the plot is “wrong,” just that they were generated using two different methods.
