Select the analysis options for Estimation Test Plan

Stat > Reliability/Survival > Test Plans > Estimation > Options
Assume shape (Weibull) or scale (other distributions) is known

Select if you know the shape (Weibull) or scale (other distributions) parameter. If you select this option, Minitab assumes that you do not need to estimate this parameter. Therefore, a smaller sample size is required. For the exponential distribution, Minitab assumes a Weibull distribution with shape parameter of 1, which is equivalent to an exponential distribution.

Confidence level

Enter a confidence level between 0 and 100. Usually a confidence level of 95% works well. A 95% confidence level indicates that you can be 95% confident that the interval contains the true population parameter. That is, if you collected 100 random samples from the population, you could expect approximately 95 of the samples to produce intervals that contain the actual value for the population parameter (if all the data could be collected and analyzed).

A lower confidence level, such as 90%, produces a narrower confidence interval and may reduce the sample size or testing time that is required. However, the likelihood that the confidence interval contains the population parameter decreases.

A higher confidence level, such as 99%, increases the likelihood that the confidence interval contains the population parameter. However, the test may require a larger sample size or a longer testing time to obtain a confidence interval that is narrow enough to be useful.

Confidence interval

From the drop-down list, select One-sided or Two-sided to indicate the number of bounds on the confidence interval. Use a one-sided confidence interval when you want to obtain only an upper bound or only a lower bound for the estimate. A one-sided interval generally requires fewer observations and less testing time to be statistically confident about a conclusion. Many reliability standards are defined in terms of the worst-case scenario, which is represented by a lower bound.

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