Determine sample size requirements for estimating parameters

To estimate the sample size that you need to estimate the scale parameter (Weibull or exponential distribution) or the location parameter (other distributions), use an estimation test plan. Use the plan to calculate the sample size you need to estimate the corresponding percentile of the distribution.

  1. Choose Stat > Reliability/Survival > Test Plans > Estimation.
  2. Under Parameter to be Estimated, choose Percentile for percent, then enter a percentage between 0 and 100.
    For example, estimating the location parameter for the normal distribution is equivalent to estimating the 50th percentile of that distribution. To estimate the location parameter for the normal distribution, enter 50.
    Use the following table to determine the percent that corresponds to the scale or location parameter for the chosen distribution.
    Distribution Parameter to estimate Percent
    Normal μ 50%
    Lognormal exp(μ) 50%
    Logistic μ 50%
    Loglogistic exp(μ) 50%
    Smallest extreme value μ 1 - e(-1) ≈ 63.2121%
    Weibull θ 1 - e(-1) ≈ 63.2121%
    Exponential θ 1 - e(-1) ≈ 63.2121%
  3. In Precisions as distances from bound of CI to estimate, choose Upper bound or Lower bound and enter the precision you would like.
  4. In Assumed distribution, choose a distribution.
    To estimate the location parameter for a normal distribution, choose Normal.
  5. Under Specify planning values for two of the following, enter one value for the exponential distribution or two values for the other distributions.
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