Work sample

1. WORK
SAMPLING
JITENDER KUMAR

Roll No: 14

2. FLOW OF PRESENTATION
Brief overview of work measurement
Work sampling

3. WORK MEASUREMENT
Methodology to develop standard times needed to
perform operations. 
Time standards have been defined as the time
required by an average skilled operator, working
at a normal pace, to perform a specified task
using a prescribed method, allowing time for
personal needs, fatigue, and delay.

4. WORK SAMPLING
Concept
Definition
Principle
Terms used
Procedure
Examples
Advantages and disadvantages
Application

5. CONCEPT
L.H.C. Tippet in 1934 for studying activities in
the cotton industry.
A technique for estimating the proportion of time
that a worker or machine spends on various
activities and the idle time.
Work sampling is a commonly used industrial
engineering technique designed to measure
how resources such as people, machines,
facilities, or equipment are used.
The work sampling objective is to assess selected
aspects of an organization's operations. To find
the frequency of occurrence of every work
element.

6. CONTD…
Brief observations of workers or machines.
At random intervals.
To estimate the allocation of time on various
activities.
Not the timing but the nature of the activity.
Then based on the findings in this sample,
statements can be made about the activity.
The standards derived from work sampling
might specify the proportion of time that should
be devoted to specific activities rather than the
amount of time required to perform a task.

7. DEFINITION
Work Sampling, (also referred to as random
sampling or activity sampling) is a work
measurement technique where observations
about work are collected at discrete time
intervals, either periodic or random.
Work sampling is broadly defined as the
application of statistical sampling techniques to
the study of work activities.

8. PRINCIPLE
Statistically, when a sufficient number of
discrete samples are observed, the overall
percentage occurrence of the samples begins to
approach actual percentage of time that each
activity takes.
Work sampling projects were traditionally
carried out manually using a paper and random
number tables.
Issues involved:
What level of statistical confidence is desired in the results?
How many observations are necessary?
When should the observations be made?

9. TERMS USED IN SAMPLING
Survey area (universe)
Preliminary survey (probe)
 Knowledge workers
 Physical workers
 Group sampling
 Individual sampling
 Observation
 Observation time

10. CONTD…
 Nonworking activity
 Working activity
 Undesirable working activity
 Confidence level
 Precision range

11. WORK SAMPLING
PROCEDURE

12. WORK SAMPLING
PROCEDURE
The selected worker should be representative
of the group and should be familiar with
standardized work methods.
The workers and supervisors should be
notified of the purpose of the study.
Identify the specific activities or
workers that are the main purpose for
the study:

13. CONTD….
Determine the number of observations to
be made:
i. Determine the confidence level.
ii. Set the accuracy limits.
iii. Apply the following formula.

Plan the sampling procedure:

14. CONTD…

where,
N

=Number of observations to be made
Z =Number of standard deviations associated
with a given confidence level
p =Estimated proportion of time that the activity
being measured occurs
E =Absolute error that is desired
2
2
)1(
E
ppZ
N
-
=

15. CONTD…
Determining the time to make
observations:
 Random observations
 Use of a random number table. For
example, a work sampling study is to be
conducted over a 1- week period of five 8-
hour workdays, the total number of
minutes would be (60 x 8 x 5) = 2400
minutes. A four-digit column of random
number could be used to select numbers
between 0000 and 2400.

16. CONTD…
 In case of few observations, some form of
alarm watch or other system is used.
 The number of observations to be taken is
usually divided equally over the study period.
For example, if 500 observations are to be made
over a 10 day period, observations are usually
scheduled at 50 per day.

17. CONTD…
Take the observations
At two or three intervals during the study
period, recompute the required sample size by
using the data collected so far. Adjust the
number of observations if appropriate.

18. CONTD…
Compute the normal time per part
(%of time working) (performance rating)
number of units produced
Compute the standard time per part
normal time + allowances
Convert the work sampling observations
into proportions and calculate desired
standard time estimates:

19. EXAMPLE
In a work sampling study, a mechanic was
found to be idle for 20% of the time. Find out
the number of observations needed to
conform to the above figures with a
confidence level of 95% and a relative error
level by + 5%.

20. SOLUTION
number of observations required:
N = Z^2p q
E^2
Where,
E = absolute error ( s x p )
p = percentage of idling
q = percentage of activity ( 1 – p)
Z = coefficient of the confidence level
( 1.96 for 95% confidence)

21. CONTD..
Hence,
N = (1.96)^2 (0.2)(0.8)
(0.05 x 0.2)^2
= (3.84)(0.16)
(0.010)^2
= 0.61
0.0001
= 6100 observations.

22. EXAMPLE
The following are the results of a work sampling study:
Observation period (in hours) 300 hours
Units processed 27000 parts
Workers working during
observation time
1600
Workers idle during observation
time
400
Performance rating 80%
Allowances 10%
Find the standard number of units the worker should process in an
hour.

23. SOLUTION
Thus, actual working hours out of 300 hours =
80% of 300 = 240 hours.
State Number Of
Observations
Percentage
Working workers 1600 1600/2000 = 80
Idle workers 400 400/2000 = 20
Total 2000 100

24. CONTD…
Normal time = actual time x performance rating
100
= ( 240 x 80 )/ 100
= 192 hours
Allowances @10% in 300 hours = 30 hours
Standard time = 192 + 30
= 222 hours
Standard number of units produced per hour =
27000/ 222
= 122 parts

25. ADVANTAGES
It is a less expensive procedure.
Observers with minimal specialized training can
conduct the sampling.
It is an effective means of collecting facts that
would not normally be collected by other means.
Several operators or machines may be observed
simultaneously by a single observer.
No mechanical device needed.

26. CONTD…
It results in less anxiety and agitation
among workers.
There is minimal interference with the
worker's normal routine.
It measures the utilization of people and
equipment directly.
A work sampling study may be
interrupted at any time without affecting
the results.

27. DISADVANTAGES
 It is not economical for studying a single
operator or machine, or for studying
operators or machines located over wide
areas.
 It cannot provide a much detailed
information .
The operator may change his or her work
pattern upon sight of the observer.
It is of little value in helping to improve
work methods.

28. CONTD…
A lot of groundwork is required.
A work sampling study made of a group
obviously presents average results, and there
is no information as to the magnitude of the
individual differences.

29. SUITABILITY
Group activities,
Non-Repetitive activities with long cycle times
(example: maintenance operator, support
personnel, etc.),
Activities that are not rigidly constrained from
the time standpoint,
Heterogeneous activities.

30. APPLICATIONS
For ratio delay studies.
To indicate the nature of the distribution of work
activities within a gang operation.
To estimate the percentage of utilization of
groups of similar machines or equipment.
To determine the productive and non- productive
utilization of clerical operations.
To measure performance.
To indicate how materials handling equipments
are being used.

31. CONTD…
To provide a basis for indirect labor standards.
To determine the standard time for a non-
repetitive operation as an alternative to the stop
watch period.
To determine the allowances for inclusion in
standard times.

32. CONCLUSION

“ A work measurement technique whereby
random observations are made for non-repetitive
activities so as to disclose underutilized workers,
poor worker discipline, overstaffing, inadequate
training, inefficient plant layout, excessive delays
(caused by poor planning, material scheduling, or
tooling), or other deficiencies.”

33. THANK YOU !!!!