| Journal: |
Computer Modeling in Engineering & Sciences
Tech Science Press
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Volume: |
144
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| Abstract: |
Parametric survival models are essential for analyzing time-to-event data in fields such as engineering
and biomedicine. While the log-logistic distribution is popular for its simplicity and closed-form expressions, it often
lacks the flexibility needed to capture complex hazard patterns. In this article, we propose a novel extension of the
classical log-logistic distribution, termed the new exponential log-logistic (NExLL) distribution, designed to provide
enhanced flexibility in modeling time-to-event data with complex failure behaviors. The NExLL model incorporates
a new exponential generator to expand the shape adaptability of the baseline log-logistic distribution, allowing it to
capture a wide range of hazard rate shapes, including increasing, decreasing, J-shaped, reversed J-shaped, modified
bathtub, and unimodal forms. A key feature of the NExLL distribution is its formulation as a mixture of log-logistic
densities, offering both symmetric and asymmetric patterns suitable for diverse real-world reliability scenarios. We
establish several theoretical properties of the model, including closed-form expressions for its probability density
function, cumulative distribution function, moments, hazard rate function, and quantiles. Parameter estimation is
performed using seven classical estimation techniques, with extensive Monte Carlo simulations used to evaluate and
compare their performance under various conditions. The practical utility and flexibility of the proposed model
are illustrated using two real-world datasets from reliability and engineering applications, where the NExLL model
demonstrates superior fit and predictive performance compared to existing log-logistic-based models. This contribution
advances the toolbox of parametric survival models, offering a robust alternative for modeling complex aging and failure
patterns in reliability, engineering, and other applied domains.
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