Economic designs of attribute control charts for multiple assignable causes

In 1981, Professor Isaac N. Gibra presented two production models for maintaining current control of an industial process subject to a multiplicity of assignable causes. The first model allows for shutting down the process during the search for the assignable cause. The second assumes that the process is allowed to continue in operation during the search for the assignable cause. In this article, two simple and explicit equations are developed for ν (sampling interval) in terms of n (sample size) and c (the acceptance number) for the two models, respectively. The paper concludes that the present models are not only more accurate, more applicable and more flexible, but also simpler to solve than Gibra’s models.