THE COPPERBELT UNIVERSITY
BSP 334- Productivity Methods II
Monday: SB 2 -Time: 14:00hrs-16:00hrs.
Tuesday: SB LT 2-Time: 08:00hrs-10:00hrs.
Prepared and presented by : Collins Mudenda
OSM Department
School of Business
18.08.2014
After performing a time study, the practitioner is left in suspense
regarding the time a worker or machine is engaged in work
activity and the time spent idling.
Therefore, it is inevitable for the practitioner to move a step further
and determine the percentage time the worker or machine is
engaged in productive time so that the reason for under
performance can identified.
This can be done using activity sampling also known as work
sampling or "ratio-delay study“ or "random observation method", or
"snap-reading method" and or "observation ratio study"
Work sampling is a method of finding the percentage
occurrence of a certain activity by statistical sampling
and random observations.
Work sampling is the process of making sufficient random
observations of an operator’s activities to determine the
relative amount of time the operator spends on the various
activities associated with the job.
The major goal of work sampling is to determine how long, or
how much of the work day, is spent on specific types of work.
Work sampling may identify the fact that certain operators spend
a large portion of their time waiting for work, or performing
paperwork tasks, or even performing activities that are not
included in their job descriptions.
There are statistical formulas to help determine how many
observations should be made.
FAIR SKILL : 1. Seem quite well trained but not good
enough. 2. Know the tolls and the environment quite well. 3.
There is some planning before doing the movement. 4. Lack
of self confidence. 5. Seem not fit the job, but already doing
that job for long time. 6. Know what to do and what must do,
but seem not too sure. 7. Most of the time wasted due own
error. 8. If does not do the work seriously, the output will be
low. 9. Usually there is no hesitating in doing movements.
POOR SKILL : 1. Unable to coordinate hands and mind. 2.
Stiff movements. 3. Hesitation in the arrangement of the
movements. 4. Seem not trained to the relevant work. 5. Not
suited for the job. 6. Hesitate doing the movements. 7. Often
do some error. 8. There is no self confidence. 9. Unable to
take own initiatives
Effort for the worker can also be divided into six categories
as shown below:
EXCESSIVE EFFORT : 1. The speed is excessive. 2. Effort
was given earnestly, but can be endangering own health.
3. Unable to maintain the speed during the working hour.
EXELLENT EFFORT : 1. Obviously high working speed. 2.
The movements are more efficient than ordinary labors. 3.
Full of attention on the work. 4. Give some advice. 5. Accept
suggestions and guidance with pleasure. 6. Bellieve in the
goodness of time measurement. 7. Unable to maintain more
couple of days. 8. Proud of the excess. 9. Rarely done the
wrong movements. 10. Sistematic. 11. Smooth movement
which is hard to follow.
GOOD EFFORT : 1. Working rhythmitically. 2. Idle time was
rare, and even there was no idle time. 3. Full of attention on
the work. 4. Pleased with the work. 5. Good working speed
and able to maintain it during the working hour. 6. Believe in
the goodness of the measurement time. 7. Accept the
suggestions and guidances with pleasure. 8. Can give
advices for work improvement. 9. Arranging the workplace.
10. Use the proper tools. 11. Maintain the tools properly.
AVERAGE EFFORT : 1. Better than poor. 2. Stable work. 3.
Accept the suggestions but do nothing about it. 4. Set Up is
done well. 5. Planning activity.
FAIR EFFORT : 1. Feel annoy with the suggestions.
2. There is no attention to the work. 3. Not taking the job
seriously. 4. Do not use enough power. 5. There was a slight
deviation from the standard ways of work. 6. Not always use
the best tools. 7. Lack of attention with the work. 8. Too
careful. 9. Systematic ways of work is average. 10. There
are unplanned movements.
POOR EFFORT 1. Too much waste time. 2. Not interest in
working. 3. Do not want take suggestions from the others. 4.
Lazy and too slow doing the job. 5. Do some ineffective
movements while doing the work. 6. The workplace is not
neat. 7. Not concerned with the tools. 8. Change the layout
of the work place that has been set. 9. Set Up work is
unwell.
CONDUCTING THE STUDY
It is recommended that a uniform procedure should be followed to
perform a work sampling study to
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.
3. Identify the Measure of Output
4. Establish a Time Period
5. Define the Activities
6. Determine the Number of Observations Needed
7. Schedule the Observations
8. Record the Raw Data
9. Summarize the Data
Establishing confidence levels
•
To achieve this we can change our calculations and obtain:
p
σ
p
p
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
σ
•
95 per cent confidence level or 95 per cent of the area under the curve = 1.96
99 per cent confidence level or 99 per cent of the area under the curve = 2.58
99.9 per cent confidence level or 99.9 per cent of the area under the curve = 3.3
σ
–
–
–
p
To make things easier, it is more convenient to speak of a 95 per cent confidence level than of a
95.45 per cent confidence level.
σ
•
Determination of sample size
statistical method
Statistical method
nomogram 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.
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).
Nomogram
method
An easier way to
determine sample
size is to read off
the number of
observations
needed directly
from a nomogram
such as the one
reproduced
in figure 91.
Making random observations
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.
Making random observations
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
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 eighthour 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).
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:
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.
Work Sampling Observation Form
Advantages of Work Sampling
Can be used to measure activities that are impractical to measure
by direct observation
Multiple subjects can be included
Requires less time and lower cost than continuous direct
observation
Training requirements less than DTS or PMTS
Less tiresome and monotonous on observer than continuous
observation
Being a subject in work sampling is less demanding than being
watched continuously for a long time
Disadvantages and Limitations
Not as accurate for setting time standards as other work
measurement techniques
Usually not practical to study a single subject
Work sampling provides less detailed information about work
elements than DTS or PMTS
Since work sampling deals with multiple subjects, individual
differences will be missed
Workers may be suspicious because they do not understand the
statistical basis of work sampling
Determining Standard Time: Rated
Activity Sampling
Disadvantages and Limitations
Example 1:
Consider an assembly line worker working 8hrs per day and
producing 420 pieces. Use the additional data on the following slide
to determine the standard time per piece.
Determining Standard Time
Information
Data Source
Daily Data
Determining Standard Time
Determining Standard Time