Work Measurement

Definition

Work measurement is the application of techniques designed to establish the

time for a qualified worker to carry out a task at a defined rate of working.

It is worth noting, however, that the term "work measurement", which we have
referred to as a technique, is really a term used to describe a family of
techniques, any one of which can be used to measure work, rather than a single
technique by itself.

A qualified worker is one who has acquired the skill, knowledge and other
attributes to carry out the work in hand to satisfactory standards of quantity,
quality and safety.
Work study
How the total time of a job is made up?
Basic and added work content
How management techniques can reduce ineffective time?
Purpose of Work Measurement

 The total time of manufacture of an article was increased by undesirable

features of the product itself, by a poorly designed process and by
ineffective time added in the course of production and by actions due to the
human element.

 All these factors tended to reduce the productivity of the enterprise.

 Work measurement is concerned with investigating, reducing and

subsequently eliminating ineffective time, that is time during which no
effective work is being performed.
Uses of Work Measurement

In the process of setting standards it may be necessary to use work measurement:

1. To compare the efficiency of alternative methods. Other conditions being equal,

the method which takes the least time will be the best method.

2. To balance the work of members of teams, in association with multiple activity

charts, so that, as nearly as possible, each member has a task taking an equal
time to perform.

3. To determine, in association with worker and machine multiple activity charts,

the number of machines an operative can run.
Uses of Work Measurement

In the process of setting standards it may be necessary to use work measurement:

The time standards, once set, may then be used:

4. To provide the basis for production planning and control for the choice of a
better layout and for process planning.
5. To provide information that can enable estimates to be made for tenders, selling
prices and delivery dates.
6. To set standards of machine utilization and labour performance which can be
used for any of the above purposes and as a basis for incentive schemes.
7. To provide information for labour-cost control and to enable standard costs to be
fixed and maintained.
Basic Procedure

1. SELECT the work to be studied.

2. RECORD all the relevant data relating to the circumstances in which the
work is being done, the methods and the elements of activity in them.
3. EXAMINE the recorded data and the detailed breakdown critically to
ensure that the most effective method and motions are being used and
that unproductive and foreign elements are separated from productive
elements.
4. MEASURE the quantity of work involved in each element, in terms of time,
using the appropriate work measurement technique.
5. COMPILE the standard time for the operation, which in the case of stop-
watch time study will include time allowances to cover relaxation,
personal needs, etc.
6. DEFINE precisely the series of activities and method of operation for
which the time has been compiled and issue the time as standard for the
activities and methods specified.
Techniques of Work Measurement

The following are the principal techniques by which work measurement is carried
out:

1. Work Sampling
2. Structured Estimating
3. Time study
4. Predetermined Time Standards (PTS)
5. Standard Data
Techniques of Work Measurement

The following are the principal techniques by which work measurement is carried
out:
Work Sampling

 Work sampling is a method of finding the percentage occurrence of a certain

activity by statistical sampling and random observations.

 Work sampling (also known as "activity sampling", "ratio-delay study“,

"random observation method", "snap-reading method" and "observation ratio
study") is, as the name implies, a sampling technique.

 When the sample size is large enough and the observations made are indeed
at random, there is quite a high probability that these observations will reflect
the real situation, plus or minus a certain margin of error.
 Work Sampling

To describe the curves we use two attributes: x, which is the average or measure
of central dispersion; and σ, which is the deviation from the average, referred to
as standard deviation.

Since in this case we are dealing with a proportion, we use σp to denote the
standard error of the proportion.

The area under the curve of normal distribution can be calculated:

one σp on both sides of x gives an area of 68.27 per cent of the total area.
two σp on both sides of x gives an area of 95.45 per cent.
three σp on both sides of x gives an area of 99.73 per cent.

We can put this in another way and say that, provided that we are not biased in
our random sampling, 95.45 per cent of all our observations will fall within x ±2σp
and 99.73 per cent of all our observations will fall within x±3σp.
Work Sampling

Curve of normal distribution

 Work Sampling

To make things easier, we try to avoid using decimal percentages; it is more convenient
to speak of a 95 per cent confidence level than of a 95.45 percent confidence level.

To achieve this we can change our calculations and obtain:

 95 per cent confidence level or 95 per cent of the area under the curve = 1.96 σp
 99 per cent confidence level or 99 per cent of the area under the curve = 2.58 σp
 99.9 per cent confidence level or 99.9 per cent of the area under the curve = 3.3 σp

In this case we can say that if we take a large sample at random we can be confident
that in 95 per cent of the cases our observations will fall within ±1.96 σp.

In work sampling the most commonly used level is the 95 per cent confidence level.
Work Sampling

Statistical Method

The formula used in this method is:

Work Sampling

Statistical Method

Let us assume that some 100 observations were carried out as a preliminary study
and at random, and that these showed the machine to be idle in 25 per cent of the
cases (p = 25) and to be working 75 per cent of the time (q = 75).

We thus have approximate values for p and q; in order now to determine the value
of n, we must find out the value of σp.

Let us choose a confidence level of 95 per cent with a 10 per cent margin of error
(that is, we are confident that in 95 per cent of the cases our estimates will be ± 10
per cent of the real value).
Work Sampling

Statistical Method

At the 95 per cent confidence level:

In other words, if we
reduce the margin of
error by half, the
sample size will have to
be quadrupled.
 Work Sampling

Nomogram Method

An easier way to determine sample size is

to read off the number of observations
needed directly from a nomogram.

Taking our previous example, we draw a

line from the "percentage occurrence"
ordinate p (in this case 25-75) to intercept
the "error (accuracy required)" ordinate
(say, 5 per cent) and extend it until it meets
the "number of observations" ordinate n,
which it intercepts at 300 for the 95 per
cent confidence level. This is a very quick
way of determining sample size.
Work Sampling

Making random observations

To ensure that our observations are in fact made at random, we can use a random
table. 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.
Let us assume that in this case we pick, the number 11 which is in the second block,
fourth column, fourth row. 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

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.
Making random observations

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.
Making random observations

Determining the sequence of time for random observations

Thus the smallest number (05) represents the fifth ten-minute period after the
work began at 7 a.m. Thus the first observation will be at 7.50 a.m. and hence on.
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.

The observations aim at detecting one of two possibilities only:

Conducting the Study

Determining the scope of the study:

We can extend this simple model to try to find out the cause of the stoppage of the
machine:
Work Sampling

Check Sheet

There is one more step to take: that of making and recording the observations
and analyzing the results.

In making the observations, it is essential from the outset that the work study
person is clear about what is to be achieved and why.

Ambiguity should be avoided when classifying activities.

Example of a
simple work
sampling
record sheet
Work Sampling

Check Sheet

Work sampling record sheet showing machine utilization and

distribution of idle time
Structured Estimating

People have always used the basis of past experience to predict future events. The
accuracy of estimating depends on the experience of the estimator in the field in
which he or she is estimating.

Structured estimating techniques are an attempt to make use of this fact and at the
same time to impose a structure and a discipline on the estimating process so that
results derived from it can be treated with confidence.

The advantages of estimating are that:

It is cheap to apply, and hence may be the only technique appropriate to one-off
jobs.
It can be used to predict times for work which has not been observed and thus
can be used as a basis for price estimating for large, one-off jobs.

Estimating is normally used where the required time values are not required in great
detail.
Structured Estimating

Analytical Estimating:

 Analytical estimating is a combination of estimating and synthesis from standard

data.

 The technique is based on the fact that if jobs are broken down into constituent
elements and individual elements are measured or estimated, errors in those
individual times will be random and will compensate for one another to leave an
overall time that will be within acceptable limits.
Structured Estimating

Analytical Estimating:

The estimating is normally carried out by a worker who is skilled in the area of work
being measured , the estimator then:

 breaks a job into elements;

 applies any standard or synthetic data that are available;
 carries out measurement on elements which are considered to warrant such
effort and expenditure;
 estimates any remaining elements using his or her experience and
knowledge of the working conditions, safety factors, etc.

Element times which are estimated may then be incorporated into the standard data
for future use, although such data should be revalidated at intervals.
Structured Estimating

Comparative Estimating:

 Comparative estimating relies on the identification and measurement of

"benchmark" jobs of known work content against which all other jobs to be
measured are compared.

 The benchmark jobs are selected to represent the whole range of work involved
and to represent intermediate points on the overall scale of job.

 These benchmark jobs are measured with some precision using an established
work measurement technique.
Structured Estimating

Comparative Estimating:

 Because of the high set-up cost of this system (in terms of measuring all the
benchmark jobs, training estimators, and so on), comparative estimating is most
suitable for situations where there is a lot of long-cycle, non-repetitive work.

 A common area of application is in maintenance work, where the work is similar

but no two jobs may be identical.

 To reduce the set-up time, it is possible to "import" data on benchmark jobs from
another organization (such as a consulting firm).

 If this is done, it is important to validate the data (as with any imported standard
data) in its field of operation through carrying out some comparative studies.
Advantages of Work Sampling

1. Many operations or activities, which are impractical or costly to measure by

time study, can readily be measured by work sampling.
2. A simultaneous work sampling study of several operators or machines may be
made by a single observer. Ordinarily an analyst is needed for each operator or
machine when continuous time studies are made.

3. It usually requires fewer man-hours and costs less to make a work sampling
study than it does to make a continuous time study. The cost may be as little as
5 to 50 percent of the cost of continuous time study.

4. Observations may be taken over a period of days or weeks, thus decreasing the
chance of day-to-day or week-to-week variations affecting the results.
Advantages of Work Sampling

5. It is not necessary to use trained time study analysts as observers for work
sampling studies unless performance sampling is required. If a time standard or a
performance index is to be established, however, then an experienced time study
analyst must be used.

6. A work sampling study may be interrupted at any time without affecting the
results.

7. Work sampling measurements may be made with a pre-assigned degree of

reliability. Thus, the results are more meaningful to those not conversant with
the methods used in collecting the information.
Advantages of Work Sampling

8. With work sampling the analyst makes an instantaneous observation of the

operator at random intervals during the working day, thus making prolonged time
studies unnecessary.

9. Work sampling studies are less fatiguing and less tedious to make on the part of
the observer.

10. Work sampling studies are preferred to continuous time studies by the operators
being studied. Some people do not like to be observed continuously for long
periods of time.

11. A stop watch is not needed for work sampling studies. If an electronic data
collector is used the results are shown on a computer printout.
Disadvantages of Work Sampling

1. Ordinarily work sampling is not economical for studying a single operator or

machine, or for studying operators or machines located over wide areas. The
observer spends too much time walking to and from the work place or walking
from one work place to another. Also, time study, standard data, or
predetermined time data are preferred for establishing time standards for short-
cycle repetitive operations.

2. Time study permits a finer breakdown of activities and delays than is possible
with work sampling. Work sampling cannot provide as much detailed
information as one can get from time study.

3. The operator may change his or her work pattern upon sight of the observer. If
this occurs, the results of such a work sampling study may be of little value.
Disadvantages of Work Sampling

4. 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.
5. Management and workers may not understand statistical work sampling as
readily as they do time study.
6. In certain kinds of work sampling studies, no record is made of the method used
by the operator. Therefore, an entirely new study must be made when a method
change occurs in any element.
7. There is a tendency on the part of some observers to minimize the importance of
following the fundamental principles of work sampling, such as the proper
sample size for a given degree of accuracy, randomness in making the
observations, instantaneous observation at the pre-assigned location, and
careful definition of the elements or subdivisions or work or delay before the
study is started.
Thank You