Table of percentiles for Regression with Life Data

The table of percentiles provides the age by which a percentage of the population is expected to fail. Use these values to determine whether your product meets reliability requirements, or to compare the reliability of two or more product designs.

The table of percentiles consists of the following columns:
  • Percent, which is the percentage of a population that is expected to fail.
  • Predictors, which indicate the combination of factor settings for that prediction.
  • Percentile, which is the age by which a percentage of the population is expected to fail.
  • Standard error, which is a measure of the variability in the estimate.
  • 95% confidence interval, which provides a range of values that are likely to contain the true value of the parameter.

Use these values only with an appropriate model for the data. If the model fits the data poorly, then these estimates may not be accurate.

Example output

Table of Percentiles Standard 95.0% Normal CI Percent Design Weight Percentile Error Lower Upper 1 Standard 5.0 134.911 17.6574 104.385 174.363 1 Standard 7.5 117.113 16.0279 89.5591 153.144 1 Standard 10.0 101.663 16.3830 74.1295 139.423 1 New 5.0 273.214 36.8022 209.819 355.763 1 New 7.5 237.171 32.6878 181.028 310.726 1 New 10.0 205.882 32.8675 150.568 281.518 5 Standard 5.0 178.749 16.9676 148.404 215.300 5 Standard 7.5 155.168 14.1107 129.836 185.443 5 Standard 10.0 134.698 15.4568 107.568 168.670 5 New 5.0 361.994 36.0778 297.761 440.084 5 New 7.5 314.239 28.8741 262.450 376.247 5 New 10.0 272.783 30.6102 218.928 339.887

Interpretation

For the compressor data, the table of percentiles includes the following results:
  • Row 1 and Row 7 refer to the combination of a standard design and a projectile weight of five pounds. For this combination, 1% of failures are expected to occur before 134.911 hours, and 5% of failures are expected to occur before 178.749 hours.
  • Row 4 and Row 10 refer to the combination of a new design and a projectile weight of five pounds. For this combination, 1% of failures are expected to occur before 273.214 hours and 5% of failures are expected to occur before 361.994 hours.

These results indicate that a compressor case with the new compressor design survives longer than a compressor case with the standard compressor design.

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