The discrete additive Weibull distribution: A bathtub‐shaped hazard for discontinuous failure data

The discrete additive Weibull distribution: A bathtub‐shaped hazard for discontinuous failure data

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Article ID: iaor20124427
Volume: 106
Issue: 2
Start Page Number: 37
End Page Number: 44
Publication Date: Oct 2012
Journal: Reliability Engineering and System Safety
Authors: , , ,
Keywords: statistics: distributions
Abstract:

Although failure data are usually treated as being continuous, they may have been collected in a discrete manner, or in fact be discrete in nature. Reliability models with bathtub‐shaped hazard rate are fundamental to the concepts of burn‐in and maintenance, but how well do they incorporate discrete data? We explore discrete versions of the additive Weibull distribution, which has the twin virtues of mathematical tractability and the ability to produce bathtub‐shaped hazard rate functions. We derive conditions on the parameters for the hazard rate function to be increasing, decreasing, or bathtub shaped. While discrete versions may have the same shaped hazard rate for the same parameter values, we find that when fitted to data the fitted hazard rate shapes can vary between versions. Our results are illustrated using several real‐life data sets, and the implications of using continuous models for discrete data discussed.

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