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Publication date: 07/30/2020

Custom Relationship Example

To create a quadratic model with Log(Temp) for the Weibull location parameter and a log-linear model with Log(Temp) for the Weibull scale parameter, follow these steps:

1. Select Help > Sample Data Library and open Reliability/

2. Select Analyze > Reliability and Survival > Fit Life by X.

3. Select Hours and click Y, Time to Event.

4. Select Temp and click X.

5. Select Censor and click Censor.

6. Select Weight and click Freq.

7. Select Custom as the Relationship from the list.

8. In the entry field for μ, enter 1, log(:Temp), log(:Temp)^2.

(The 1 indicates that an intercept is included in the model.)

9. In the entry field for σ, enter 1, log(:Temp).

10. Select the check box for Use Exponential Link.

11. Deselect the check box for Nested Model Tests.

12. In the entry field for Use Condition, enter 10.

13. Select Weibull as the Distribution.

Figure 4.24 shows the completed launch window using the Custom option.

Note: The Nested Model Tests check box is not checked for non-constant scale models. Nested Model test results are not supported for this option.

14. Click OK.

Figure 4.24 Custom Relationship Specification in Fit Life by X Launch Window 

Figure 4.25 shows the location and scale transformations, which are subsequently created and included at the bottom of the Estimates report section.

Analysis proceeds similarly to the Example of the Fit Life by X Platform, where the Arrhenius Celsius Relationship was specified.

Figure 4.25 Weibull Estimates and Formulas for Custom Relationship 

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