This presentation is lucid and self explanatory about the fundamentals of work sampling .

1. Work Sampling
By:
Shivank K. Shah -1115100
 Samir A. Mehta -1115096
Rushikesh Gaikwad-1115092

2. Work Sampling Origin

3. Uses of Work Sampling

4. Basis of Work Sampling

5. Basis of Work Sampling (cont.)
• Based on an event being present or not.
• Probability of x occurrences of an event in n observations: (p +
q)n = 1
• Expand IAW binomial theorem, with the 1st term giving the
probability of x=0, the 2nd term x=1, etc…
• This distribution of probabilities is known as the binomial
distribution, with the Mean = np, and Variance = npq.
• As n becomes large, the binomial distribution approaches the
normal distribution

6. Example
• Take 5 coins
• Toss each of the coin in one set.
• Count number of time a given combination of head and tail is
obtained.
• Combination : 0 No. head and 5 No. of tail.
• Combination : 1 No. head and 4 No. of tail.
• Combination : 2 No. head and 3 No. of tail.
• Combination : 3 No. head and 2 No. of tail.
• Combination : 4 No. head and 1 No. of tail.
• Combination : 5 No. head and 0 No. of tail.
• Repeat tossing for 100 time of a set of
five coins.

7. Example (cont):
The probability distribution for the number
of heads and tails is as follows

8. Example (cont.)

9. Finding the number of observations

10. Example 2: Finding no. of observations

11. Solution by Nomogram(Graphical) method

12. CONDUCTING A STUDY
• It is recommended that a uniform procedure should be
followed to perform a work sampling study .It is as follows:
1. Establish the Purpose
• First, the objective of the study should be established. Work
sampling can be used to determine an overall perspective on
the work done.
2. Identify the Subjects
• Second, the people performing the task must be identified,
i.e. general office work is being studied with the objective of
determining overall productivity.

13. Conducting a study(cont.)
3. Identify the Measure of Output
• The third step in making the study is the identification of the measure of
the output produced or the types of activities performed on the jobs being
studied. This step is especially important if the objective of the study is to
measure productivity with the intent of setting a standard.
4. Establish a Time Period
• Fourth, the time period during which the study will be conducted must be
established. Starting and stopping points for the study must be defined as
well.
5. Define the Activities
• This step involves defining the activities that are performed by the people
under study. For example, the definition used in a machine utilization
study, including only the categories of working, idle, and idle-mechanical
breakdown.

14. Conducting a study(cont.)
6. Determine the Number of Observations Needed
• After the work elements are defined, the number of observations for
the desired accuracy at the desired confidence level must be
determined. If a reasonable guess cannot be made, then a trial study of
perhaps 20 to 40 observations should be made to get an estimate.
7. Schedule the Observations
• Once the number of required observations has been determined, either
from appropriate statistical calculations or from tables, and the actual
observations must be scheduled. Typically, the analyst will assign an
equal number of observations each day during the course of the study.
For example, if 800 observations are required and 20 work days are
established as an appropriate observation time, 40 observations should
be recorded each day.
• A random number table can be used to establish the random times for
each observation.

15. Making random observations(Example)
• To ensure that our observations are in fact made at random, we can use
a random table such as the one in table 12.
• Various types of random table exist, and these can be used in different
ways. In our case let us assume that we shall carry out our observations
during a day shift of eight hours, from 7 a.m. to 3 p.m. An eight-hour day
has 480 minutes. These may be divided into 48 ten-minute periods.
• We can start by choosing any number at random from our table, for
example by closing our eyes and placing a pencil point somewhere on
the table. Let us assume that in this case we pick, by simple chance, the
number 11 which is in the second block, fourth column, fourth row (table
12).
• We now choose any number between 1 and 10. Assume that we choose
the number 2; we now go down the column picking out every second
reading and noting it down, as shown below (if we had chosen the
number 3, we should pick out every third figure, and so on).
• 11 38 45 87 68 20 11 26 49 05

17. • Looking at these numbers, we find that we have to discard 87, 68 and 49 because
they are too high (since we have only 48 ten-minute periods, any number above
48 has to be discarded).
• Similarly, the second 11 will also have to be discarded since it is a number that has
already been picked out. We therefore have to continue with our readings to
replace the four numbers we have discarded. Using the same method, that is
choosing every second number after the last one (05), we now have 14 15 47 22
• These four numbers are within the desired range and have not appeared before.
Our final selection may now be arranged numerically and the times of observation
throughout the eight-hour day worked out. Thus our smallest number (05)
represents the fifth ten-minute period after the work began at 7 a.m. Thus our first
observation will be at 7.50 a.m., and so on (table 13).

18. Conducting a study(cont.)
8. Inform the Personnel Involved
• Before the study is actually performed, the personnel involved
should be informed about the objective of the study and the
methodology that will be employed.
9. Record the Raw Data
• The next is the actual recording of the raw data. Although this
recording can be performed by anyone, it is desirable that a
trained analyst be employed.
• It is also very important that the observations be made at exactly
the same location every time.
10. Summarize the Data
• After the data have been collected, they must be summarized.

19. Example: Conducting the study
• Determining the scope of the study. Before making our actual observations, it is
important that we decide on the objective of our work sampling.
• The simplest objective is that of determining whether a given machine is idle or
working. In such a case, our observations aim at detecting one of two
possibilities only:
• We can, however, extend this simple model to try to find out the cause of the
stoppage of the machine:

20. Making the observations
• So far we have taken the first five logical steps in conducting a work
sampling study.
– selecting the job to be studied and determining the objectives of the
study;
– making a preliminary observation to determine the approximate
values of p (idle) and q (working);
– in terms of a chosen confidence level and accuracy range, determining
n (the number of observations needed) determining the frequency of
observations, using random tables;
– designing record sheets to meet the objectives of the study.
– There is one more step to take: that of making and recording the
observations and analyzing the results.

22. Work Sampling Observation Form

23. Time standard using Work Sampling
• For example, 8-hour day as a drill-press operator. A work sampling study might
show 15% idle or 72 minutes (480*0.15=72) and 408 minutes (480*0.85)
at an average performance index of 110 percent.
During the day 420 pieces are produced.

24. Advantages of Work Sampling
• Economical
• Many operators or activities which are difficult or uneconomical to
measure by time study can readily be measured by work sampling.
• Two or more studies can be simultaneously made of several
operators or machines by a single study person. Ordinarily a work
study engineer can study only one operator at a time when
continuous time study is made.
• It usually requires fewer man-hours to make a work sampling study
than to make a continuous time study. The cost may also be about a
third of the cost of a continuous time study.
• No stopwatch or other time measuring device is needed for work
sampling studies.
• It usually requires less time to calculate the results of work
sampling study. Mark sensing cards may be used which can be fed
directly to the computing machines to obtain the results just
instantaneously.

25. Advantages of Work Sampling(cont.)
• Flexible
• 6. A work sampling study may be interrupted at any time without affecting the
results.
• 7. Operators are not closely watched for long period of time. This decreases
the chance of getting erroneous results for when a worker is observed
continuously for a long period, it is probable that he will not follow his usual
routine exactly during that period.
• Less Erroneous
• 8. Observations may be taken over a period of days or weeks. This decreases
the chance of day-to-day or week-to-week variations that may affect the
results.
• Operators Like It
• 9. Work sampling studies are preferred to continuous time study by the
operators being studied. Some people do not like to be observed continuously
for long periods of time.
• Observers Like It
• 10. Work sampling studies are less fatiguing and less tedious to make on the
part of time study engineer.

26. Disadvantages of Work Sampling
• Work sampling is not economical for the study of a single operator
or operation or machine. Also, work-sampling study may be
uneconomical for studying operators or machines located over wide
areas.
• Work sampling study does not provide elemental time data.
• The operator may change his work pattern when he sees the study
person. For instance, he may try to look productive and make the
results of study erroneous.
• No record is usually made of the method being used by the
operator. Therefore, a new study has to be made when a method
change occurs in any element of operation.
• Compared to stop watch time study, the statistical approach of
work sampling study is difficult to understand by workers.

27. Case Study 1:Salespeople

28. Case Study 2:Assembly line employee