stagelife 0.1.0

Initial release.

stagelife implements the stage life testing (SLT) model of Laumen & Cramer (2019), “Stage life testing”, Naval Research Logistics 66(8):632-647, doi:10.1002/nav.21874 – a two-stage cumulative-exposure life-testing model in which units begin on a baseline stress and, at a fixed change-point, some or all surviving units move to an elevated stress.

• Twelve baseline lifetime distributions (Weibull, Power Lindley, Exponentiated Lindley, Exponentiated Exponential, Marshall-Olkin Exponential, Lomax, Exponentiated Teissier, Log-Logistic, Chen, Log-normal, Gamma, and Power Muth), each with closed-form density, distribution, and quantile functions.
• Three parameter-sharing cases (common, shape1, shape11) for the elevated-stage shape parameter.
• Data generation under the random-withdrawal design, with both fixed-proportion and fixed-count selection rules, via rslt(); the classical simple-step-stress design is the prop_transfer = 1 special case.
• Maximum likelihood estimation via fit_slt(), with standard print(), summary(), coef(), vcov(), logLik(), AIC(), and BIC() methods.
• Asymptotic (Wald) and bootstrap (non-parametric and parametric; percentile, bootstrap-t, and log-scale bootstrap-t) confidence intervals.
• Design-planning tools (slt_prob_stage1()), Kolmogorov-Smirnov goodness-of-fit testing with a parametric-bootstrap correction (slt_gof_ks()), likelihood-ratio tests between nested cases (slt_lrt()), and AIC/BIC model comparison across fits (slt_model_comparison()).
• Diagnostic plots: fitted CDF, survival, P-P, and Q-Q.
• Four bundled real step-stress data sets.

See vignette("stagelife-intro") for a full worked example.

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