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With the growth of the apparel sector over a period of time, Industrial Engineering (IE)practices are gaining popularity and benefiting the organizations through providingscientific yet simple and practical solutions like time study, method study and PMTS. Worksampling is one such practical techniques which has some unique characteristics that makeit immensely useful to the management, highlighting the true picture of the shop floorfunctioning, by measuring time consumed on non productive activities of an operator withminimal money, manpower and time involvement.

It has been observed that in India most of the organizations don’t follow work sampling as akey tool for optimizing apparel manufacturing operations, the reasons for this may be thedifficulties faced in practicing it on the shop floor, involvement of statistics with which peopleare not comfortable and the nature of jobs being done or the kind of production ordersbeing executed. Manoj Tiwari, Assistant Professor at NIFT, Gandhinagar discusses thebasics of work sampling, procedure of conducting the study, advantage and limitations, andthe factors affecting the work sampling results through exercises done on the shop floor atvarious production houses.

Work Sampling in ApparelManufacturing

Work sampling is one of the work measurement techniques similar to time study with stop watch and

data synthetics using PMTS (Pre-determined Motion and Time Systems), capable of highlighting thepercentage of occurrences of time consumed in an activity, which prima-facie is non-productive or

ineffective in nature and can help the management take necessary actions to curb such inefficiencies. On

the other hand, work sampling also highlights the amount of time spent in productive (for examplesewing), associated or support activities; thus by using work sampling, factors affecting the operator

productivity can also be identified.

Conducting time study is a cumbersome and costly process which consumes a significant amount ofobserver’s time, while work sampling is a simple yet pragmatic approach based on the theory of

probability, following the statistical sampling and random observations. Work sampling is just the

“degree to which the event(s) is likely to occur”.

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Work sampling observations need a significant amount of planning and preparatory work before

conducting the same on the shop floor. A clear-cut identification of all the objectives is one of the primary

requirements of this study which highlights why exactly the study needs to be done and what is expectedfrom such study. Pre-planning also requires a thorough discussion of all the aspects related to the

project in detail prior to conducting work sampling, with the people and authorities associated with it. The

objective is to get people in confidence by explaining the pros and cons of the study as well as convincingthem with clear explanation about the possible impact of the study on the organization.

Sample Size DeterminationCritical to the entire work sampling

method is the determining of how

many times the observations need to

be taken based on a confidence leveland the percentage error or degree of

accuracy using a direct Nomogram

(refer Figure 1). Confidence levelsignifies the number of times the test

results are within a specified range,

whereas the accuracy level meansdegree of closeness of

measurements of a quantity to that

quantity’s actual (true) value. 95 per

cent confidence level with 5 per centaccuracy level means in 95 per cent

of the cases when test is conducted,

the result will be between +/- 5 percent of the actual value. For example,

if there is a result which is 55 at 95%

confidence level and +/- 5 per cent

error, the actual value will swing

between +/- 5 per cent of 55.

Classifying Observations

Deciding about the times, when the

observer is going to take the

observations on the floor is purely

random in nature so that any kind of

bias can be avoided while makingthe observation. In addition, for an

error free study, various activities of

an operator should be broken down

to smaller visually measurable

movements of body parts (elements),

each of which needs to be clearly

described and classified.

In order to avoid subjectivity, it is

critical that the level of understanding

of all the people involved in the study

should be uniform while deciding the

elements, as the entire results and

inferences depend solely on thebreak-up of the activities.

To begin with the generic nature of

activities needs to be decided, like

productive activities, personal

activities and avoidable andunavoidable delays. Productive

activities are the activities which

contribute directly in the productivity of

the work like sewing. These may be

divided into main activities and

associated activities, while stitching

is main activity when needle isworking (that’s the real productive

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working (that’s the real productive

activity), activities like untie the

bundle, taking piece to the needle

point, folding, aligning, guiding, etc.

are associated activities. Personal

activities are individual physiologicalpersonal needs like drinking water

and going to washroom, relaxing, etc.

Avoidable delays are the activities,

which are primarily non value added

and don’t contribute in productivity

enhancement. These are

responsible for inefficiencies in theproduction process. Sitting idle

without any reason, waiting for

material or work, speaking to

cooperators, roaming around,

machine maintenances which are

unplanned, etc. can be classified as

avoidable delays. Unavoidabledelays are the activities which may

not be completely avoided, like

bundle handling, changing the

needle and bobbin thread, needle

replacement, changing work-aids,

organizing the work place, etc.

The operator on a sewing floor may

be involved in various activities

related to stitching, material handling,

recording the production,

communicating with supervisor,

checking the quality of the piece

stitched by him, chatting with otheroperators, repairing the machine,

replacing the thread, replacing the

needle and doing many more such

activities in the various departments

on the shop floor, right from fabric

inspection, spreading to sewing and

finishing. Apart from it, he/she may gofor short breaks for drinking water or

to go to the restroom or washroom or

may be just sitting idle or waiting for

the material. Classification of all such

actual activities should be done very

carefully as observation on thesepoints will show the real picture and

will guide for decision making and

improvements.

Conducting Work Sampling

Once the number of observationsrequired is statistically derived, and

timings of observations, as well as

the standard format (on which

observations need to be taken) are

ready, one is ready to proceed for the

work sampling study. The observer

needs to go to the floor on the

particular pre-defined times, observe

and mark the individual operator in

one go without spending any time,

and fill the information in astandardized format with clearly

defined classifications of activities.

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The format (refer Figure 3, Work Sampling Format) may change from organization to organization

depending on the situation.

This is the reason that work sampling is also called snapreading or flash-reading. The observer just

needs to take a glance and put tally marks in the work sampling format under the observed category of

the activity against the respective operator code in the format. The same system needs to be followed

whenever the observer revisits the floor for the study.

Analysing Results

Once the study is over, each operator’s data needs to be compiled to know the percentage share of

individual activities from the total number of observations.

The results may give the idea about how much time (in percentage) is consumed in which all activities

and subsequently corrective actions can be taken. The work sampling exercise is recommended for

repetition every 3-4 months for checking the effectiveness of measures taken and analyse the

improvements.

Benefits of Work Sampling over Time Study

• It helps in the determination of standard times that should be allowed for various activities.

• It helps in determination of percentage allowances required for personal needs, fatigue andunavoidable delays, etc.

• Work sampling is economical and capable of producing the same results as time study at 1/3rd to 1/6th

of the time and cost, as it is based on operator’s view point or probably factual results from his

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of the time and cost, as it is based on operator’s view point or probably factual results from his

experience.

• Longer time periods can be studied based on the convenience (does not require analyst to make

continuous observations of observer) where time study needs uninterrupted time to observe. As the

person in case of work sampling just walks through the line, observes each activity at a glance and goes

back to his seat, whereas in time study the person needs to stand continuously in front of an operator and

measure using stop watch.

• Operator is not subject to continuous observation.

• Many operations and workers can be studied by a single analyst.

Limitations of Work Sampling

• The work sampling results may not be applicable for the small order quantities, as there may bechances that the production order is over during the study. In this case the results may not be authentic

and reliable.

• Time study is capable of providing a finer breakdown of activities and delays while work sampling

cannot provide as much detailed information of individual operator.

• The observation timings should be purely random. In case it’s not followed and observer enters into the

floor after regular intervals; operators may change the work style. Hence the result may not be realistic

and useful.

• Involvement of statistics makes the work sampling difficult to understand and apply, and people hesitate

in using the work sampling.

• The work sampling results may vary when the method is changed, for example level of automation while

stitching, method of material handling (usage of over-head material handling systems), type of product,

etc.

ConclusionWork sampling technique is capable of providing new insights if followed religiously and scientifically.

Prima facie it looks difficult to understand and conduct but in real sense the technique is fast, easy and

economical. In fact, it is very useful to the people who want to get a glimpse of the activities without getting

involved in the technical intricacies. The technique is very much capable of highlighting the needle time,

which is the only productive activity in real sense while stitching.

There are global benchmarks available for percentage of time consumed in various activities in the

garment manufacturing shop floor which are guides for standard times allocation for various delays yet

these standards cannot be adopted straight forward.

There are many factors which need to be considered depending on the working conditions of that

particular country or region which make it more relevant and practically applicable. Some of these factorsmay be cited as level of technology used, product type and volume of orders. For the advanced new

generation machines, where automation level is high and human intervention is minimal, the needle time

should be high as the machines are programmed for each activity and performs tasks automatically

based on the commands given.

At the same time there is very minimal time consumed in material handling, positioning, data recording,

thread replacement, etc. Product type is another area which affects the needle time in a factory. For

example if one factory produces bed sheets where seam lengths are comparatively longer than that of

garments like T-shirts or shirts. Lesser stops in the sewing of a seam are observed which may lead to

increased the percentage of needle time.

At the same time if the factory produces garments where high level of skill is required (such as high

fashion tops with some hand work, etc.) with precision, then there are fair chances that percentage of

needle time may go down and personal, fatigue and delay levels may go high. High volume orders whichhave more number of units to be produced may have increased the percentage of needle time, as the

system might have achieved the rhythm and overcome the start-up, losses.

While in case of small orders there are chances that by the time system achieves its peak after start-up,

the order quantity is finished from stitching. In this case work sampling standards are of no use

practically.

In context of Indian garment industry, so far no such study has been reported where needle times for

different products (at different technology levels covering different apparel production setups) have been

observed and studied. Such data may give us insights regarding the percentage of time utilized in sewing

and other activities as well as the factors affecting the needle time with its logical justification.

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