ACCEPTANCE SAMPLING

The objective of acceptance sampling is to take decision whether to accept or reject a lot based

on sample’s characteristics. The lot may be incoming raw materials or finished parts.

An accurate method to check the quality of lots is to do 100% inspection. But, 100%

inspection will have the following limitations:

The cost of inspection is high.

Destructive methods of testing will result in 100% spoilage of the parts.

Time taken for inspection will be too long.

When the population is large or infinite, it would be impossible or impracticable to inspect

each unit.

Hence, acceptance-sampling procedure has lot of scope in practical application. Acceptance

sampling can be used for attributes as well as variables.

Acceptance sampling deals with accept or reject situation of the incoming raw materials and

finished goods. Let the size of the incoming lot be N and the size of the sample drawn be n.

The probability of getting a given number of defective goods parts out a sample consisting of n

pieces will follow binomial distribution. If the lot size is infinite or very large, such that when a

sample is drawn from it and not replaced, then the usage of binomial distribution is justified.

Otherwise, we will have to use hyper-geometric distribution.

Specifications of a single sampling plan will contain a sample size (n) and an acceptance

number C. As an example, if we assume the sample size as 50 and the acceptance number as

3, the interpretation of the plan is explained as follows: Select a sample of size 50 from a lot and

obtain the number of defective pieces in the sample. If the number of defective pieces is less

than or equal to 3, then accept the whole lot from which the sample is drawn. Otherwise, reject

the whole lot. This is called single sampling plan. There are several variations of this plan.

In this process, one will commit two types of errors, viz., type-I error and type-II error. If

the lot is really good, but based on the sample information, it is rejected, then the supplier/

producer will be penalized. This is called producer’s risk or type-I error. The notation for this

error is α. On the other hand, if the lot is really bad, but it is accepted based on the sample

information, then the customer will be at loss. This is called consumer’s risk or type-II error. The

notation for this error is β. So, both parties should jointly decide about the levels of producer’s

risk (α) and consumer’s risk (β) based on mutual agreement.

OPERATING CHARACTERISTIC CURVE (O.C. CURVE)

The concepts of the two types of risk are well explained using an

The quality circles begun in Japan in 1960s. The concept of quality circles is based on the

participating style of management. It assumes that productivity will improve through an uplift of

morale and motivations which are in turn achieved through consultation and discussion in informal

groups. One organizational mechanism for worker participation in quality is the quality circle. It

is typically an informal group of people that consists of operators, supervisors, managers and so

on who get together to improve ways to make the product or deliver the service.

According to Juran, quality circle defined as “a group of work force level people, usually

from within one department, who volunteer to meet weekly (on company time) to address quality

problems that occur within their department.”

Quality circle members select the problems and are given training is problem-solving

techniques. A quality circle can be an effective productivity improvement tool because it

generates new ideas and implements them. Where the introduction of quality circle is

capably planned and where the company environment is supporting they are highly

successful.

The benefits fall into two categories: those are measurable saving and improvement in the

attitudes and behaviour of people. Quality circles pursue two types of problems, those concerned

with the personal well being of the worker and those concerned with the

Quality Circles Effect on Individual Characteristics

(a) Quality circles enable the individual to improve personal capabilities—group participation

and learning specific problem-solving tools.

(b) Quality circles increase the individual’s self-respect.

(c) Quality circles help worker change certain personality characteristics—shy person become

as active.

2. Quality Circles Effect on Individuals Relations with Other

(a) Quality circles increase the respect of the supervisor for the worker.

(b) Quality circles increase workers understanding of the difficulties faced by supervisors—

problem selection, solving and implementations.

(c) Quality circle increase management’s respect for worker.

3. Quality Circles Effect on Workers and Their Attributes

(a) Quality circles change some workers negative attitudes.

(b) Quality circle reduces conflict stemming from the working environment.

(c) Quality circles help workers to understand better the reasons while many problems

solved quickly.

Quality circles, as a management tool, are based on the following basic principles of

people:

(a) People want to do a good job.

(b) People want to be recognized as intelligent, interested employees and to participate in

decisions affecting their work.

(c) People want information to better understand goals and problems of their organizatiwell being of company