Specify Design Details | JMP 13.2

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Design of Experiments Guide • Accelerated Life Test Designs • Accelerated Life Test Plan Window • Specify Design Details

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Specify Design Details

Specify the factor levels, details of the prior distribution, the time range and probability of interest, and the length of the test and number of units to be tested.

Distribution Details

Enter the settings for the acceleration factors.

Distribution Choice

Select a life distribution (Weibull or LogNormal) for each acceleration factor. For more information, see Statistical Details.

Enter prior estimates of the acceleration model parameters. The prior estimates are hyperparameters in a Bayesian prior distribution. The Prior Mean values can be a best guess based on subject matter knowledge or they can be based on a previous study.

Prior Variance Matrix

Enter values for the variances and covariances of the prior distribution for the acceleration model parameters. These variances and covariances reflect uncertainty relative to the prior estimates of the acceleration model parameters. Large variances indicate greater uncertainty.

Ignore prior variance

Select this option to ignore the prior variances and covariances for the prior distribution. When these variances and covariances are ignored, the design is created by treating the values entered under Prior Mean as the true parameter values. This design is close to optimal if the prior mean parameters are close to the true values. However, this design is not robust to misspecification of the parameter estimates. If you are unsure about your prior estimates, use the Prior Variance Matrix to reflect your uncertainty.

Diagnostic Choices

Specify values used to construct Time I-Optimal and Probability I-Optimal designs. See ALT Optimality Criterion. Enter values for the following:

Time range of interest

Specify the time interval over which you want to estimate the fraction of the population that is failing. Enter the lower value in the left box and the upper value in the right box. If you are interested in a specific time point, enter that value in both boxes.

Probability of interest

Specify the failure fraction for which you want an estimate of time. For example, if you want to estimate the time at which 10% of the units fail, then enter 0.10.

Specify values relating to the length of the test, inspection intervals, and the number of units being tested. Enter values for the following:

(Available only for Continuous Monitoring.) Length of time during which units will be on test. When you make the design table, record each unit’s failure time or whether it was right censored.

Inspection Times

(Available only for Monitoring at Intervals.) Times at which inspections are conducted. When you make the design table, these times are used to construct Start Time and End Time columns. The number of units failing in each interval is recorded.

Number of units under test

The number of units in the experiment.

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If you are designing an initial experiment, enter the number of units that you plan to test.

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If you are augmenting a previous experiment, enter the number of units tested in the previous experiment plus the number of units for the next experiment.

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Help created on 9/19/2017