Sample size table - sample sizes for Estimation Test Plan

Use the sample size table to choose the sample size necessary to estimate a percentile or reliability with the specified amount of precision.

If you provided a right-censoring time in the Right Cens subdialog box, Minitab displays this value as the censoring time.

The precision is the distance between your percentile or reliability estimate and the upper (or lower) bound of the 1-sided confidence interval for that estimate. If you provide multiple values for the precision, Minitab displays them in separate rows of this table.

The sample size is the number of units you must test to obtain that level of precision. Because the sample size must be rounded to the nearest integer value, you cannot exactly achieve your target confidence level. Minitab displays the actual confidence level for that sample size, which is slightly higher than the target confidence level.

Example output

Estimation Test Plans

Type I right-censored data (Single Censoring) Estimated parameter: 10th percentile Calculated planning estimate = 393.094 Target Confidence Level = 95% Precision in terms of a one-sided confidence interval that gives a lower bound for the parameter. Planning Values Percentile values 500, 1000 for percents 12, 20
Planning Distribution Distribution Scale Shape Weibull 6464.18 0.803708
Test Plans Actual Censoring Sample Confidence Time Precision Size Level 1000 100 354 95.0011 1000 200 61 95.0892 1000 300 15 95.1695

Interpretation

For the insulation data, with a censoring time of 1000 hours and a target confidence level of 95% for a 1-sided confidence interval, you must test the following:
  • 354 units to estimate a lower bound for the 10th percentile within 100 hours with 95.0011% confidence
  • 61 units to estimate a lower bound for the 10th percentile within 200 hours with 95.0892% confidence
  • 15 units to estimate a lower bound for the 10th percentile within 300 hours with 95.1695% confidence
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