ACCEPTANCE SAMPLING
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Acceptance Sampling
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ACCEPTANCE SAMPLING
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Table of Contents
Abstract/Introduction .................................................................................................................................... 3
Acceptance Sampling.................................................................................................................................... 4
Relationship between acceptance sampling and the improvement of quality ........................................... 4
Advantages of acceptance sampling ......................................................................................................... 5
Disadvantages of acceptance sampling ..................................................................................................... 6
Acceptance sampling plans ....................................................................................................................... 6
Single sampling ..................................................................................................................................... 7
Double sampling ................................................................................................................................... 7
Sequential sampling .............................................................................................................................. 8
Operating characteristics curves ........................................................................................................... 9
References ................................................................................................................................................... 10
ACCEPTANCE SAMPLING
Abstract/Introduction
Product quality assurance is notably a major problem for industrial engineering.
Nonetheless, there is the need to ensure compliance in regard to the minimum standards in
product manufacturing so as to augment design performance capability. It is at this instance
where acceptance criteria as well as acceptance sampling come into play. Particularly,
acceptance sampling is a principle component of quality control. It is a useful tool utilized when
the testing costs are higher in comparison to the cost of passing a defective item or in some
instances when the testing of the product is destructive. Therefore, it is notable that acceptance
sampling is a compromise when it comes to choosing between 100% inspection and no
inspection at all (Wetherill, 2013). The research paper will detail the definition of acceptance
sampling, its relationship with quality improvement, the pros and cons of acceptance sampling,
and acceptance sampling plans.
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Acceptance Sampling
Acceptances sampling can be termed as a statistical measure that is utilized in quality
control. Most of the organizations are not in a position to test all their products, probably due to
large volumes or the potential for ruining of destructing the products. Therefore, acceptance
sampling helps solve this consideration through the testing of sample of products to check for
any defects. It is a statistical process that involves testing of batch size, sample size and detailing
the number of defects that can be acceptable within a batch. Through this process, an
organization is in a position to measure the quality of a batch with a specified statistical certainty
without the need to test every product units. Using the t-statistic, the statistical reliability can be
measured for accuracy purposes (Wetherill, 2013).
Relationship between acceptance sampling and the improvement of quality
Most people might question how organizations have the ability to ensure that suppliers
are in compliance with the critical quality standards. In most instances, organization have their
reliance on inspection for the incoming materials. The results of the delivery are compared to the
quality standards of the organization whereby if they do not conform to the acceptable standards,
they are rejected (Mitra, 2016).
Majorly, organizations utilize acceptance sampling procedures and are critical in the
minimization of the inspection costs, helps in the management of risks and the prevention of
non-conforming quality features from having their entry into the production process. It can be
said that acceptance sampling is somewhere between no inspection and 100% inspection.
Acceptance sampling plans are utilized as sources of quality data. In this case, there is the use of
Pareto charts, statistical analytical tools, histograms, and control charts in the analysis of the use
of inspection data. A comparison is usually made between the suppliers. This way, there is the
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identification of substantial time-based changes in parts with regard to per million defect rates. If
there is a lack of control or any control in the processes of the suppliers, then it is identified
(Mitra, 2016).
Therefore, such information is useful in ensuring a collaborative effort between suppliers
and organizations in enhancing the quality of products. Essentially, utilization of the
measurement data along with either accepting or rejecting shipment allows acceptance sampling
procedures to complement the emblematic improvement efforts. The specific supplier quality
levels are accurately quantified and such information is utilized significantly to improve supplier
quality as well as the reduction of quality costs when it comes to the supplier chain (Mitra,
2016).
Advantages of acceptance sampling
Acceptance sampling procedures are widely utilized in organizations that produce large
volumes of products. This is due to the fact that an organization utilization an already set
production procedure. Besides, acceptance sampling is economical and is utilized under the
assumptions when the quality characteristics of an item are under control and there is
homogeneity in production. It is, therefore, evident that acceptance sampling saves time as well
as money and resources in the overall evaluation of the quality of products. The savings brought
about by acceptance sampling can be measured in terms of the reduction in labor, the reduction
in the product part movement and a short product manufacturing inspection throughout. There is
no complicated training for those involved in acceptance sampling procedures and since they can
be easily imparted training. Few staff are also involved in the inspection process. In the cases of
destructive products, they can be easily inspected through the use of acceptance sampling.
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Moreover, with acceptance sampling, it involves a quick inspection process. In this case,
scheduling and delivery times are improved. Also, computation work in the statistical measure is
comparatively very small. There is still less fatigue and boredom in the acceptance sampling
procedures. Finally, acceptance sampling procedures put more pressure to the suppliers to ensure
quality improvement efforts are enhanced rather than the rejection of items.
Disadvantages of acceptance sampling
Acceptance sampling has its limitations. First, the conclusion on the quality of the
products is usually based on the sample size selected. In this case, there is a high probability of
making the wrong inference with regard to the overall quality of the products. This risks goes
down to the producers and the consumers (Aslam, Kundu & Ahmad, 2010).
Besides, the success of the scheme is dependent on the sample randomness, the quality
features of the products being tested and the criteria being utilized for acceptance sampling.
Without proper and accurate assessment, it can lead to the wrong inferences on the nature and
the quality of the products delivered. This has an implication that there is no 100% assurance that
the specifications of the products are in order. This, thus, increases the probability of drawing
wrong inference with regard to the quality of the batch sampled (Aslam, Kundu & Ahmad,
2010).
Acceptance sampling plans
Particularly, items can be inspected in different ways. The acceptance sampling plan is
usually defined by the lot size, the sample size and the acceptance number (Rao, Durgamamba &
Kantam, 2014).The sampling plans are a way of offering the producer’s and the consumer’s risk.
The available sampling plans include;
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Single sampling
A single sampling plan is a type of decision rule where rejecting or accepting a lot size is
dependent on the results of a single random sample from the lot. In this case, the random sample
size is taken and each item is inspected. In the cases where the number of defects identified do
not go beyond the sample size, the consumer can accept the lot size. Therefore, the defects
identified can be repaired or rejected and hence returned to the producer. At the instances where
the number of defects is higher than what is expected, the consumer can subject the entire
products to 100% inspection or decide to reject the entire lot and take it back to the producer. It
is the easiest acceptance sampling plan that can be used (Rao, Durgamamba & Kantam, 2014).
Figure 1: Single sampling demonstrated
Double sampling
In double sampling, it is the work of the management to give two sample sizes as well as
two acceptance numbers. At the instances where the quality of the lot is very good, the consumer
can accept the lot on the basis of the first sample. On the other hand, where the quality of the lot
is bad, the consumer can reject the lot still on the basis of the first sample. With the use of double
sampling, it aids in the reduction of the inspection costs in comparison to the single-sampling
ACCEPTANCE SAMPLING
plan. However, this applies for the lot sizes that have either low or high proportion defective.
This is because there is the option of making a decision after taking a first sample (Rao,
Durgamamba & Kantam, 2014).
Sequential sampling
Sequential sampling is seen as a refinement of the double sampling plan. There is the
random selection of items from the lot size. These are inspected one by one. When an item is
inspected, a decision can be made to reject the lot size, accept the lot size and continue with
sampling. These decisions are usually based on the cumulative results for the random samples.
The individual inspecting usually plot the number of defectives against the cumulative sample
size. When the number of defects are less than the given acceptance number, the consumer is
usually free to accept the lot. However, in the instances where the number of defects are greater
than the given acceptance, the consumer is supposed to reject the lot. At times, the number
derived for the acceptance criteria can be between the two instances. In this case, there is the
requirement to ensure the inspection of another item (Fallah Nezhad, Akhavan Niaki & Abooie,
2011).
Figure 2: Sequential sampling demonstrated
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Operating characteristics curves
The figure below shows a typical operating characteristics curve
Figure 3: typical operating characteristics curve
The operating characteristics curve details how well an acceptance plan differentiates
between the good and the bad lot sizes. It is a specific plan. It combines the acceptance level with
the sample size. The function of the operating characteristic curve is to indicate the probability
that the plan will accept different lots of different quality levels (Rao, Durgamamba & Kantam,
2014).
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References
Aslam, M., Kundu, D., & Ahmad, M. (2010). Time truncated acceptance sampling plans for
generalized exponential distribution. Journal of Applied Statistics, 37(4), 555-566.
Fallah Nezhad, M. S., Akhavan Niaki, S. T., & Abooie, M. H. (2011). A new acceptance
sampling plan based on cumulative sums of conforming run-lengths. Journal of
Industrial and systems engineering, 4(4), 256-264.
Mitra, A. (2016). Fundamentals of quality control and improvement. John Wiley & Sons.
Rao, R. S., Durgamamba, A. N., & Kantam, R. R. L. (2014). Acceptance Sampling Plans: Size
Biased Lomax Model. Universal Journal of Applied Mathematics, 2(4), 176-183.
Wetherill, G. B. (2013). Sampling inspection and quality control (Vol. 129). Springer.
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