Negative location parameter

[Gerhard Hoch]

in an investigation (welding failures on a machine) i tried to observe over 3 days the results of failures. Analysing with weibull++ i got from 2 of the 3 days a recommendation to fit weibull 3 parametric. 2 of the 3 day-analyses showed negative location parameter.
What could a negative location parameter in practical give hints for?

[tarik]

A positive gamma parameter (location parameter) indicates a failure free period, meaning that the product will can not fail during that period. A negative gamma value indicates that the product is not starting with 100% reliability, meaning that you have some quality/shipping issues existing in the product even before it’s put into use. Usually a 3-parameter Weibull will fit your data better then a 2-parameter Weibull, because it has more parameters. That doesn’t necessarily mean that it’s an appropriate mode, you need to verify your assumptions if you want to accept the 3-parameter distribution.
More info can be found at: http://www.weibull.com/LifeDataWeb/three_parameter_weibull_regression.htm

[Gerhard Hoch]

thanks tarik,

the first idea i had was a memory-effect.
your description is also in that way.
probably i have to find the memory key (its a co-operatig electroniclally functioning system)