Implements statistical process control ('SPC') monitoring schemes
for heterogeneous reliability observations using Accelerated Failure Time
('AFT') models integrated with continuous gamma frailty. It accommodates both
uncensored and right-censored reliability observations in the presence of
observed and unobserved covariates. Provides Phase I maximum likelihood
estimation of Weibull 'AFT' gamma frailty model parameters, and Phase II
monitoring procedures including probability-limits-based control charts,
exponentially weighted moving average ('EWMA') charts with conditional
expected values, and likelihood-ratio cumulative sum ('CUSUM') control
charts. Competing 'CUSUM' schemes (ignoring unobserved frailty or both
covariates) and Average Run Length ('ARL') simulation utilities are also
provided. The statistical methodology is based on Asadzadeh (2022)