Acceptance sampling is a statistical technique used to inspect the quality of a batch of products. This quality control mechanism is applied to samples taken from the product batch. It involves comparing the number of defective pieces and the predefined acceptance number to accept or reject the batch.
The concept was popularised by Harold F. Dodge and Harry G. Romig from Bell Labs during World War II. The United States military then used the acceptance sampling method to test bullets. Furthermore, American statistician Walter A. Shewhart penned his work on acceptance sampling in the book "Statistical Methods from the Viewpoint of Quality Control" in 1939.
Acceptance sampling is a statistical method for evaluating if a batch of a product is fit for usage or not. In other words, it is the process of sampling applied to a whole batch of products received to determine the acceptability. The purpose is to ensure that the batch or lot meets a specific standard, which may vary depending on the company or industry.
In this methodology, random sampling is done from a group of products, and the sample products are tested. Decisions about whether to accept or reject the lot are made based on the sample test results. It is a compromise made between a complete inspection and no inspection.
Although this method aids in determining whether or not to accept a batch of a product, it is not an accurate estimation of the overall lot quality. Typically, the manufacturer gives the consumer a few samples from the lot. Then, the lot is approved by the consumer if there are fewer defects than the acceptable number.
There are three main types of the acceptance sampling plan, which are discussed below:
A single sampling strategy involves selecting a sample from the batch and testing it to see if it meets certain quality criteria. In other words, check whether the defective items are not above the acceptable limit. If the lot fails to meet the set criteria, the entire lot is rejected. This type of plan is employed for inspecting products produced in small batches.
A double sampling strategy involves selecting two samples from the lot and comparing them to see if they fulfill a predetermined quality standard. The method sets two acceptance numbers. The lot is accepted if the defective pieces are less than the smallest acceptance number (first acceptance number).
At the same time, the lot is rejected if the defective pieces are greater than the largest acceptance number (second acceptance number). A second sample is drawn if the number of defective pieces falls between the first and second acceptance numbers. Finally, the lot is accepted if the total number of defective pieces from two samples exceeds the second acceptance number.
In multiple sampling, more than two samples will be used to arrive at a decision. For example, sequential sampling can have several samples. Following the sampling of the group, the test is carried out to determine whether or not it has passed a quality criterion. If it does not exceed the threshold limit, the procedure is repeated.
Let us look at the acceptance sampling example to understand the concept better:
Manufacturer ABC Ltd sends a lot of 20,000 artificial flower bouquets to XYZ Ltd., an event management company. XYZ planned to conduct a quality check on the received bouquets. However, since inspecting and evaluating each bouquet will take time and money, they decided to use the acceptance sampling by attributes method. By using the method, XYZ Ltd strategizes a plan to inspect 30 bouquets.
Following the method, they randomly selected 60 flower bouquets from a lot of 20,000 flower bouquets. Then, they decided to accept the sample if the defective bouquets were below four. But, if there are more than three defects, XYZ Ltd. will reject the sample and sends the flower bouquets back to ABC Ltd.
Some of the significant advantages of acceptance sampling are the following:
This technique helps businesses ensure that only high-quality goods are offered to customers, increasing customer satisfaction and market base. This method can be applied in several circumstances and for different products. Furthermore, it works best when the inspection cost is very high, and the process is time-consuming.
What are acceptance sampling disadvantages?The disadvantages are that the sample size is very small compared to the lot size, so it becomes difficult to identify whether the method is appropriate for the case. In addition, there is no guarantee that every batch will meet specifications, so there is a chance of accepting bad batches.
How does acceptance sampling differ from process control?Sampling is done to check the product quality before or after the process, whereas process control is a common statistical technique to monitor and control a process to obtain the appropriate output; hence it is a process that is active throughout the production process.
This has been a guide to What is Acceptance Sampling. We explain its use in quality control, attributes, types, example, and advantages. You may also find some useful articles here:
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