Frailty models of manufacturing effects |
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Authors: | J T Wassell G W Kulczycki E S Moyer |
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Institution: | (1) National Institute for Occupational Safety and Health, 26505 Morgantown, WV |
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Abstract: | The median service lifetime of respirator safety devices produced by different manufacturers is determined using frailty models to account for unobserved differences in manufacturing processes and raw materials. The gamma and positive stable frailty distributions are used to obtain survival distribution estimates when the baseline hazard is assumed to be Weibull. Frailty distributions are compared using laboratory test data of the failure times for 104 respirator cartridges produced by 10 different manufacturers tested with three different challenge agents. Likelihood ratio tests indicate that both frailty models provide a significant improvement over a Weibull model assuming independence. Results are compared to fixed effects approaches for analysis of this data. |
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Keywords: | Survival analysis Cox regression random effects Weibull distribution |
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