Economic design of variable sampling intervals EWMA charts with sampling at fixed times using genetic algorithms

Control charting is a graphical expression and operation of statistical hypothesis testing. In the present paper, we develop the economic design of the exponentially weighted moving average (EWMA) chart using variable sampling intervals with sampling at fixed times (VSIFT) control scheme to determine the values of the six test parameters of the chart (i.e., the sample size, the fixed sampling interval, the number of subintervals between two consecutive sampling times, the warning limit coefficient, the control limit coefficient, and exponential weight constant) such that the expected total cost per hour is minimized. The genetic algorithms (GA) are applied to search for the optimal values of the six test parameters of the VSIFT EWMA chart, and then an example and its solution are provided. Finally, a sensitivity analysis is carried out to investigate the effect of model parameters on the solution of the economic design. (c) 2006 Elsevier Ltd. All rights reserved.