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The MTTF (mean time to failure) is the expected time that an item will function before failure.
Sometimes it may be difficult to determine the best distribution based on the probability plot or goodness-of-fit measures. Use the table of MTTF to compare the MTTF for several selected distributions to see how your conclusions would change depending on the distribution chosen.
If several distributions provide a reasonable fit to the data and similar conclusions, then the choice of the distribution is less important.
However, if your conclusions differ depending on the distribution, you may want to report the most conservative conclusion, collect more data, or use additional information, such as process knowledge and expert advice.
| Standard Error | 95% Normal CI | |||
|---|---|---|---|---|
| Distribution | Mean | Lower | Upper | |
| Weibull | 76585.0 | 488.71 | 75633.1 | 77549 |
| Lognormal | 77989.9 | 615.96 | 76792.0 | 79207 |
| Exponential | 93707.3 | 3236.67 | 87573.5 | 100271 |
| Normal | 76966.0 | 514.76 | 75957.1 | 77975 |
Based on a Weibull distribution fitted to the muffler data, the new type of muffler can be expected to last, on average, until 76585.0 miles.
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