Measures of Reliability
When performing a prediction, several measures of reliability can be calculated. The most commonly calculated measures are described in the following topics:
• MTBF
• MTTF
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In some cases, measures of reliability are specified rather than calculated. When a value is specified, it originates from an outside source such as a part manufacturer or a databook and is generally based on laboratory or field data. If you are using specified values in a prediction, be sure to include the time necessary to obtain and validate this failure rate information.
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All MIL-HDBK-217 models, the Telcordia Issue 1 model, and all Bellcore models assume 90% confidence levels. For the Telcordia Issue 2, Issue 3, and Issue 4 models, the upper confidence level to use is specified by Telcordia upper confidence level, which appears under Prediction in the System file properties. The default is 90%. The standards for other models make no mention of confidence levels. For more information, see Prediction System File Properties.