Statistical design of np-charts with multiple control regions

Models were developed for the design of np-charts with three and four control regions, respectively. Procedures for obtaining solutions to the models were also developed. Numerical examples are given to illustrate the model and to study the properties of the charts. The results of the numerical examples show that changes in the specified values of most of the risks and powers associated with the chart--particularly those classified as 'critical risks'--affect the values of the design parameters of the charts. The OC and power curves drawn for some of the numerical examples show that the discriminatory power of an np-chart with multiple control regions depends on the values of the design parameters and the number of control regions--the more the number of its control regions, the less the discriminatory power of the chart, and vice versa.