Observed and unobserved heterogeneity in failure data analysis

In reality, failure data are often collected under diffract operational conditions (covariates), leading to heterogeneity among the data. Heterogeneity can be classified as observed and unobserved heterogeneity. Un-observed is effect of unknown, unrecorded, or missing covariates. most reliability studies, covariates neglected. This may lead inaccurate modeling, consequently, wrong operation maintenance decisions. There a lack systematic approach model covariate in analysis. paper aims present framework for analysis presence Here, will analyzed using frailty models. A case study illustrate application framework.