The effects of skewness and kurtosis of processing times in unpaced lines

Abstract

Numerous empirical studies have shown that, in unpaced lines, the stations' processing times have a variety of shapes (i.e., skewness and kurtosis))65. Thispaper investigates how the line's utilization factor is affected by these skewness and kurtosis measures. We found that positive skewness has a significant negative effect on utilization, and that the magnitude of this effect is greater if the line has more stations or less buffer capacity, or if the processing-times' cv is larger. Kurtosis also affects utilization significantly, but the effect may be negative or positive, depending upon the processing-times' skewness and the number of stations in the line. Our findings imply that when simulating long lines with small buffer capacities, it may be necessary to model more accurately the actual processing times. Also, the common practice of using normal distributions to approximate the typically positively-skewed processing times often leads to an overestimation of the actual utilization rate.