WORK SAMPLING

JITENDER KUMAR

Roll No: 14

FLOW OF PRESENTATION Brief overview of work measurement Work sampling

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.

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

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.

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.

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.

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?

TERMS USED IN SAMPLING

Survey area (universe) Preliminary survey (probe) Knowledge workers Physical workers Group sampling Individual sampling Observation Observation time

CONTD… Nonworking activity Working activity Undesirable working activity Confidence level Precision range

WORK SAMPLING PROCEDURE

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:

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:

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 activitybeing measured occurs

E = Absolute error that is desired

2

2 )1(

E

ppZN

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.

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.

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.

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:

EXAMPLEIn 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%.

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)

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.

EXAMPLEThe 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.

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

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

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.

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.

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.

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.

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.

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.

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.

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.”

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