Time Study
Abstract
The purpose of this investigation was to practice using a PDA of time studies and to learn to complete time studies. This process was completed by observing a work cycle, recording data and using the data to calculate the sample size. As a result we were able to determine how many samples must be taken to find the desired data.
Introduction
Our problem today was to determine how to properly take time studies in the work place and use the results from these studies to determine the sample size. This is important because you need to know how many samples to take and when to take them to get the information that you need. Today’s problem was investigated using the Time Study form to find the appropriate sample size.
Material and Methods
The materials need to complete today’s experiment were a workstation, a PDA with Time Study Software, a laptop computer and a Time Study Form. The following procedure was used:
- A worker was observed and timed doing five cycles of a task at a workstation
- The times were downloaded to a laptop.
- Calculations were made on the Time Study Form to find the total allowed time.
- The allowed time was used to calculate the probability of each work task category.
- A sample size was calculated.
Results
The Sample Size necessary for the shortest task was 36767. For the longest task a sample size of 11234 is necessary. The shortest task was the ID number input (element 1) and the longest was assembling the handle (element 6). The total time allowed for this job is 84.7 seconds. All times can be seen in Appendix A and probability and Sample Size equations are found in Appendix B.
Discussion
A possible source of error in this experiment is the inexperience with the tools being used. Since no one had ever used a PDA for a time study before, some observations may have been skewed due to a slowed response time in the PDA operator. We used a snapback system since the tasks were short and continuous without breaks. The sample size was calculated with the given probabilities of 1/25 for the shortest task and 3/25 for the longest task. In order to have reasonable results for a time study of the tasks performed at 95% confidence, we would need between 11,000 and 37,000 observations. Our observations were not nearly large enough to use as reliable data. The sample size could be changed by altering the confidence level desired. The equation used was n=z2*(1-p)/s2*p where s is the desired confidence level and z is the number of standard deviations required to achieve the desired confidence level. Appendix A shows the summary of data for this job. The total times are the total amount of time spent performing each task. The average T is the average amount of time spent on each task. The average time was multiplied by the level factor to find the normal time. The normal time was multiplied by 1.15 to add 15% time to account for fatigue and delays as the allowed time. All the allowed times were totaled to find the total job time allowed.
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