Why Weibull scale parameter is not used for Reliability Demonstration Test calculation?

[#1]

Hi,

The product's lifetime distribution is modeled by the Weibull distribution with scale = 44, shape = 4

In JMP Demonstration Explorer for Parametric Reliability, I input the following:

Alpha: 0.2

Distribution: Weibull

Demonstration time: 100

Demonstration Reliability: 0.98

Weibull beta: 4

Maximum failures allowed: 0

Sample size: 10

Solve for Test time = 168

Why scale parameter is not used?

Thanks.

[#2]

Hello @ZRW !

Great question! As it turns out, we don't ask for the scale parameter because we don't need it. Given the shape parameter, the demonstration time, and the demonstration reliability, we can actually compute the scale parameter quite easily. So asking for the scale parameter would be redundant. 

Check out this article on ReliaWiki: https://reliawiki.org/index.php/Reliability_Test_Design. It goes into more detail on how the test time is computed, including how you can determine the scale parameter from the other inputs. 

Hope that helps!

Caleb 

[#3 · Accepted solution]

Hi @calking 

Thank you for your input. It took me some time to go through the reference you provided. I have a much better understanding now.

Really appreciate your help.

Thanks!