TABLE OF CONTENTS The company specifications for the work measurement study state: "The proposed study design will include the methodology for assuring accuracy within 10% with a 95% confidence level based on the direct work category."
Three study criteria are important to ensuring study accuracy. These criteria are having the observation period span a sufficient portion of the year, having the observations evenly spread out over the course of the shift, and having a sufficient number of observations.
First, the study covered a period of 7 weeks which should be of sufficient duration to classify as a representative period of typical working conditions and cancel out the effect of most special, limited-duration events that may impact wrench time. Although personnel were loaned to another plant and personnel were in training at times during the study, these periods were seen as typical circumstances under which the workforce operates.
Second, keeping a check sheet ensured making an equal number of observations during each 20-minute block of the entire 10-hour shift by the end of the study. Then during the analysis of the results, a check was made of the hourly distribution of observations to determine if any skewing of data might be present. (For example, having a more than average number of observations during the traditional morning break period may cause an artificial decrease in reported wrench time.) In most cases there appeared to be an even distribution of observations. In the few instances where there was a slightly...
