The pioneer of this is L.H.C.Tippet in a British textile mill.. This also known as â€˜Work samplingâ€™ (WS).
WS is a method of finding the percentage occurrence o a certain activity by statistical sampling and random observations. This is also known by other names such as â€˜ratio delay studyâ€™, â€˜random observation methodâ€™, â€˜snap-reading methodâ€™ and â€˜observation ratio studyâ€™.
The need for Work Sampling:
In order to obtain complex and accurate picture of he productive time and idle time of the machines in a specific production area, it would be necessary to observe continuously all the machines in that area and to record when and why any of the machines were stopped. It may be impossible to do this unless a large number of workers spent the whole of their time on this task alone which may not be realistic.
If it were possible to note at a glance and at a given moment it might be found that 80% of the machines were working and 20% stopped. If this action is repeated 20 or more times at different times of the day and at each time the proportion was always 80% working machines then it may be possible to say that at any point of time there are 80% machines are working.
It is generally not possible to do this as suggested above. The next best thing that can be done is to undertake tours of the factory at random noting which machine is working and which is stopped with the reasons there of. This is the basis of work sampling technique.
Here we use a sample of observations made at random moment during a working period to indicate what goes on all the time. When he sample size is large enough and the observations made are at random there is a high probability that the observations made are close to realistic with minimum plus or minus margin of errors.
Advantages of Work Sampling in comparison with Time study:
1. Many operations which are impractical or costly to measure by time study can readily be measured by work sampling.
2. It usually requires fewer man hours and costs less to make work sampling study than it is to make continuous time study. The cost may be as low as 5 to 50% of time study.
3. It is not necessary to use trained time study analysts as only observation is required for work sampling studies unless performance sampling is required.
4. A work sampling study can be interrupted at any time without affecting the results.
5. With work sampling the analyst makes instantaneous observation of the operator at random intervals during the working day thus making prolonged time studies unnecessary.
6. Work sampling studies are less fatiguing and less tedious to make on the part of he observer.
7. WS is preferred to continuous time studies by the operators being studied. Some operators may not like to be observed continuously for long periods of time (as required for time study).
1. Time study permits a finer breakdown of activities and delays than is possible with work sampling.
2. The operator may change his or her work pattern upon the sight of the observer.
3. WS study made of groups presents average results and there is no information as to the magnitude of individual differences.
4. Management and workers may not properly understand work sampling as they do time study.
5. In certain types of work sampling no record is made of the method used by the operator. Therefore an entirely new study is required o be made when there is a change in the method.
6. There is tendency on the part of some observers to minimize proper sample size, randomness of observation etc.