STE 515: Construction Management and Technology
TOPIC: Activity Sampling
Activity sampling is the procedure which analyses and evaluates the spent work time of the
worker in a specific defined category of activity e.g. setting up a machine, assembly parts of
machine, blinding of foundation, setting out of building, formwork for beams and columns e.t.c.
It is as important as all other statistical techniques because it permits quick analysis, recognition
and enhancement of job responsibilities, tasks, performance competencies and organizational
work flows. Activity sampling is based on the statistical method first devised by Tippet in 1934.
He used this technique firstly in the British Textile Industry.
In activity sampling, a large number of observations are made of the workers over an extended
period of time. For statistical accuracy, the observations must be taken at random times during
the period of study and the period must be a true representative of the type of activities
performed by the workers. One important usage of activity sampling technique is the
determination of standard time for a manual manufacturing task. Similar technique for
calculating the standard time is the study time, standard data e.t.c.
Objectives of activity sampling
Activity sampling is a fact finding tool and has the following two main objectives:
i. To measure activities and delays when a man is working and percentage of that when
he is not working. It means a fair day’s work.
ii. Under certain circumstances, to measure manual tasks in order to establish standards
for an operation.
Theory of activity sampling
It states that the percentages of observations recorded on an operation in any state, provided
“sufficient number of observations are taken at random”. Here particular attention is placed
on random and sufficient number of observations. In this method, errors are likely to occur
but the errors tend to diminish as the number of samples increases.
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Example one
Table 1: working observations for a worker
State Total observations
Working 36
Idle 4
Table 1 shows some working observations for an operator for 8 hours. Find the percentage of
idle and working time.
Solution
% of idle time = 4⁄40 𝑥 100 = 10%
% of working time = 36⁄40 𝑥 100 = 90%
This means the worker was idle for 10% or 48 minutes of the day and working for 90% or
432 minutes of the day.
Activity sampling procedures
1. Define the problem
a. State the main objectives or purpose of the problem
b. Describe the details of each element to be measured.
2. Obtain the approval of the head of the department in which the study is to be made.
Obtain the cooperation of the operators to be studied and they should also understand the
purpose of the study.
3. Determine the desired accuracy of the final results in the form of standard error or
percentage
4. State the confidence level.
5. Make a preliminary estimate of the percentage occurrence of the activity or delay to be
measured for a day or two days. This may be estimated on the basis of past experience.
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6a. Design the study by determining the number of:
i. Observations to be made.
ii. Observations needed.
iii. Days or shift needed for the study.
b. Make plans for taking the observations such as, time for taking and the route to be
followed by the observer.
c. Design the observation forms.
7. Make the observations and record the data.
8. Summarize the data at the end of each day.
9. Check the accuracy or precision of the data.
10. Prepare the report and state results. If required make recommendations.
Application of activity sampling
1. Activity sampling can be applied for the estimation of the percentage utilization of
machine tools, crane fork trucks e.t.c.
2. Activity sampling can be also be used to estimate the unavoidable delay times for
deciding the delay allowances.
3. To estimate the percentage of the time consumed by various job activities i.e.
supervision, repairs and inspection e.t.c.
4. Activity sampling is also used to find out time standards, specially when the job is not
repetitive and where time study by stop-watch method is not possible e.g. for
maintenance works, office works, repair works, ship building e.t.c. Time standards can be
calculated by combining rating with activity sampling as illustrated in the following
example.
Example two
A work sampling study showed that 20% of a work week of 48 hours was consumed by
avoidable delays. If each time a work sampling observation was made, the operator was
rated and the average of such rating was 110%. If 100 units were produced by the
operator, calculate standard time.
Solution
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Duration of work = 48 hours
% of working time = 80% i.e. 100%-20%
Therefore, actual time worked by the operator per piece= 48x0.8/100
Now standard time =actual time per piece x rating of operator= 48/100 x0.8x1.10=0.4224
hours per unit=0.4224x60=25.344 mins
