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Dec 8, 2014 12:29 PM
(12465 views)

Can anyone suggest a way to run "Fit Life by X" when the form is

mu (log lifetime) = beta0 + X^(beta1)?

From running the reciprocal and custom relations, beta1 values between -1 and -2 seems to give the best fit to the observed failure times.

Many thanks!

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Thank you! I'll give it a try!

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The Nonlinear Model platform seems to work well. Carrying this beyond the original question, it looks as though I would need to create a 'dummy' X variable in order to combine two factors, e.g. Peck's Power-law humidity model.

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Dr. Bill Meeker also pointed out that this model's parameters can also be obtained, in a different form, by using the Box-Cox relationship in the Fit Life By X platform and then using the distribution results sensitivity profiler to maximize lambda's likelihood and then re-running Box-Cox with that lambda. (Thanks Dr. Meeker!)

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You cannot. Fit Life by X assumes the formula for mu is linear in beta's. I don't see whether this model has an equivalent form which is linear in beta's. I would suggest using Nonlinear to solve the problem.

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Re: Fit Life by X

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Thank you! I'll give it a try!

Highlighted
The Nonlinear Model platform seems to work well. Carrying this beyond the original question, it looks as though I would need to create a 'dummy' X variable in order to combine two factors, e.g. Peck's Power-law humidity model.

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Highlighted
Dr. Bill Meeker also pointed out that this model's parameters can also be obtained, in a different form, by using the Box-Cox relationship in the Fit Life By X platform and then using the distribution results sensitivity profiler to maximize lambda's likelihood and then re-running Box-Cox with that lambda. (Thanks Dr. Meeker!)

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