Enter planning information to determine the number of test units and how to allocate the units across stress levels for an accelerated life test.

The data you collect for an accelerated life test can be censored or uncensored. A time-censored test plan or failure-censored test plan often provides precise results while minimizing test costs. For more information, go to Data censoring.

- Under Parameter to be Estimated, select an option to indicate what you want to determine:
- Percentile for percent: Estimate the time at which a certain percentage of the units will fail. This value is useful for determining a warranty period for a product. Enter a value between 0 and 100 to indicate the percentage of units that will fail. The nth percentile has n% of the observations below it, and (100–n)% of observations above it.

- Reliability at time: Estimate the percentage of units that will survive a certain length of time. This value is useful for estimating how many units will survive through a warranty period. The time could be a standard time measurement, such as number of hours, or another measurement that indicates a certain amount of usage, such as number of cycles, number of weight units, and so on.

- From the drop-down list, indicate whether you want to enter a sample size or a precision value that is defined in relation to a confidence bound. For example, if you have a certain number of units available for testing, enter a sample size to determine the plan that provides the best precision for the sample size. If you have a precision goal, enter a lower bound or upper bound to determine the plan that requires the minimum number of samples needed to obtain that precision.
- Sample size: Enter one or more values to indicate the number of units available for testing.
- Lower bound: Enter a precision value to indicate the distance from the reliability estimate to the lower bound of the confidence interval (CI). The lower bound is commonly used because many reliability standards are defined in terms of the worst-case scenario. For example, if you want to estimate the 10th percentile of your failure time distribution, and the lower bound is to be no more than 25 hours less than your estimate, then select Lower bound and enter
`25`. - Upper bound: Enter a precision value to indicate the distance from the reliability estimate to the upper bound of the confidence interval (CI).

- From Distribution, select a distribution to model your data. Base your decision on process knowledge or an evaluation of the distribution fit. For more information, go to Distribution fit for reliability analysis.
- From Relationship, select an option to indicate whether to transform the accelerating variable. If you can assume a linear relationship, select Linear and no transformation is performed. To transform the accelerating variable, select Arrhenius, Inverse temp, or Ln (Power).
###### Note

For information on the distribution models and the transformations for the accelerating variable, go to Choose the appropriate model for accelerated life testing.

- In Shape (Weibull) or scale (other distributions), enter the shape parameter if you are using a Weibull distribution or the scale parameter if you are using another distribution. For the exponential distribution, do not enter a value. Minitab assumes that the shape parameter is 1.
- Specify planning values for two of the following. For example, you could provide planning values for the intercept and the slope, or for the intercept and one percentile, or for two percentiles. Minitab calculates the value of the unknown parameters.
###### Note

If you specify planning values for two percentiles, they must be at different stress levels. For more information, go to Values for estimation test plans and accelerated life test plans.

- Percentile: Enter a percentile that indicates the time at which a certain percentage of units are expected to fail. In Percent, enter a percent associated with the percentile. In Stress, enter the stress level. For example, if you expect 50% of electrical components to fail after 450 hours at a voltage of 7V, enter 450 in Percentile, 50 in Percent, and 7 in Stress.
- Percentile: Enter a percentile that indicates the time at which a certain percentage of units are expected to fail. In Percent, enter a percent associated with the percentile. In Stress, enter the stress level. For example, if you expect 15% of units to fail after 200 hours at a stress level of 5V, enter 200 in Percentile, 15 in Percent and 5 in Stress.
- Intercept: Enter the intercept for the relationship with the accelerating variable.
- Slope: Enter the slope for the relationship with the accelerating variable.

###### Note

If you have previously used accelerated life tests for similar experiments, you can use historical estimates of the slope and intercept as planning values. For more information on the slope and intercept of accelerated test models, go to Choose the appropriate model for accelerated life testing.