Estimating the shape or scale
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When running a demonstration test, it is common to have a good estimate of the shape (Weibull distribution) or scale (other distributions) parameter because this parameter is often not impacted by a redesign. However, if your assumptions regarding this value are wrong, your demonstration test plan will be flawed.

You should consider rerunning the analysis using a range of reasonable values for the assumed parameter to see how the assumed value is impacting your conclusions.