Work sampling

Definition 1:

Measuring and quantifying activities:"A measurement technique for the quantitative analysis of non-repetitive or irregularly occurring activity."


Meaning of Work Sampling

• Work sampling is based on the theory that the percentage of the number of observations on a particular activity is a reliable measure of the percentage of the total actual time spent on that activity.
• Work sampling operates by an observer taking a series of random observations on a particular "thing" of interest (machine, operating room, dock, etc.) to observe its "state" (working, idle, sleeping, empty, etc.). When enough samples are taken, an analysis of the observations yields a statistically valid indication of the states for each thing analyzed.
• Assume, for example, that you wish to determine the proportion of time a factory operator is working or idle. Also assume that 200 random observations were made of the operator and during 24 of these he or she was observed to be idle. Therefore, you find that the individual is working 176/200 = 88% of the time.

Advantages of Work Sampling

• It is relatively inexpensive to use and extremely helpful in providing a deeper understanding of all types of operations.
• When properly used, it can help pinpoint those areas, which should be analyzed in, further detail and can serve as a measure of the progress being made in improving operations.

Questions of work sampling study

• ·What is our equipment/asset utilization?
• ·When we are not adding value to the product, how are we spending our time?
• ·How are our inter-dependent systems performing?
• ·Where should we focus our continuous improvement activities?

Distinction between Work sampling and "Time Studies"

• ·Work sampling is lower cost because it uses random samples instead of continuous observations.
• ·Many operators or machines can be studied by a single observer
• ·Work sampling can span several days or weeks, thus minimizing the effects of day to day load or equipment variations
• ·Work Sampling tends to minimize operator behavior modification during observation.
• ·Work Sampling, in general, does not require a trained time-study analyst to take the observations. Also, stopwatches or other timing devices are not required. Many studies make use of off-shift technicians or operators to take the observations.

Work sampling Methodology

• An analyst RANDOMLY observes an activity (equipment, operating room, production line) and notes the particular states of the activity at each observation.
• The ratio of the number of observations of a given state of the activity to the total number of observations taken will approximate the percentage of time that the activity is in that given state.
• Note that random observations are very critical for a work sampling study. A brief example might be that 77 of 100 observations showed a machine to be running. We might then conclude, within certain statistical limits, that the equipment is operational 77% of the time.