A sequential approach to sampling design for time studies of cable yarding operations

Abstract

Comprehensive sampling design including determination of the distribution, number of observations and specification of desired levels of precision is typically ignored in time studies of yarding operations. A computer-based data collection, processing, and analysis system was developed for time studies that permits improved sampling design. Data collection programs were written for continuous timing of yarding operations and downloaded on to hand-held computers equipped with real-time clocks. After each shift of observation, the time study data are uploaded to a portable microcomputer. The data are then processed through a series of programs that provide error checking, cataloging, and formatting in preparation for analysis. Data from three cable yarding operations were used in a study to assess the potential for sequential design and to determine precision levels obtainable from short-duration time studies. Confidence intervals were computed cumulatively and used to assess whether additional observation of a specific machine on a particular site was justified. The data collection, processing, and real-time analysis system shows promise as a technique for improving sampling design of time studies for timber harvesting operations through sequential analysis of the data.