Acceptance Sampling

What exactly is Acceptance Sampling?

Acceptance sampling is a quality control statistical measure. It enables a corporation to assess the quality of a batch of items by randomly picking a number for testing. The quality of this specified sample will be considered the overall quality level for the group of items involved.

A corporation can only constantly test some of its products; testing every single unit of product in some cases is almost impossible. This is because there might be too many quantities to check at a fair cost or in a reasonable amount of time. Furthermore, extensive testing may cause the product to be damaged or rendered, making the product unsuitable for sale in some way. Thus, a little sample testing is often suggestive without jeopardizing the majority of the product run.

In-Depth Understanding of Acceptance Sampling

Acceptance sampling looks for flaws in a representative sample of the product. The procedure begins with defining the size of the product lot to be evaluated, followed by the number of goods to be sampled, and lastly, the number of faults acceptable within the sample batch.

For sampling, products are picked at random. Typically, the operation occurs at the manufacturing site before the items are sent to sellers or customers. The primary objective is to figure out the quality of a batch with a specific statistical confidence level without evaluating every single unit. The firm (that is, purchasing items from the manufacturer) decides whether to accept or reject the lot based on the results-how many of the predetermined samples pass or fail the testing.

A t-statistic, an inferential statistic used to determine if there is a significant difference between two groups that share common features, is widely used to evaluate the statistical reliability of a sample.

History

The present industrial form of acceptance sampling comes from the early 1940s. During World War II, the United States military used the testing approach to test projectiles. The concept and technique were developed by Harold Dodge, a veteran of Bell Laboratories' quality assurance department, which was hired as a consultant by the Secretary of War.

While each bullet needed to be evaluated, Dodge argued that a decision could be made about the entire lot based on a random sample. Harry Romig, with other colleagues at Bell, established a precise sampling technique to be used as a standard, detailing the sample size, the number of permitted faults, and other criteria.

Acceptance sampling techniques were prevalent during and after World War II. On the other hand, it is essential to note that acceptance sampling is not the same as acceptance quality control, as Dodge said in 1969. Acceptance sampling applies to specific lots and is a quick, short-term test, similar to a spot check, based on particular sampling procedures. Acceptance quality control, on the other hand, relates to the complete product line in a broader, more long-term meaning; it acts as an essential element of a well-designed manufacturing process and system.

What are the different types of Acceptance Sampling?

The acceptance sampling plan is classified into three categories, which are explained below:

1. Single Sampling Plan

In this approach, a sample from the batch is taken and tested to check whether it fits specified quality standards. In other words, it is ensured whether the defective items are within the acceptable limit or not. The entire lot is approved if it satisfies the established requirements. This sort of approach is used to inspect items made in small batches.

2. Double Sampling Plan

A double sampling approach is taking two samples from a batch and comparing them to see if they meet a predefined quality level. Two acceptance numbers are assigned by the procedure. If the number of faulty pieces is fewer than the smallest acceptance number (first acceptance number), the lot is accepted.

At the same time, if the number of defective components exceeds the maximum acceptability number (second acceptance number), the lot is rejected. A second sample is chosen if the number of faulty pieces falls between the first and second acceptability thresholds. The lot is authorized/ approved if the total number of problematic components from two models exceeds the second acceptance number.

3. Multiple or Sequential Sampling Plan

More than two samples will be used to decide during the multiple sampling, and sequential sampling may include many samples. Following group sampling, the test is performed to assess whether or not the group met a quality standard. If the procedure does not exceed the threshold limit, it is repeated.

What are the advantages of Acceptance Sampling?

Acceptance sampling can be used to investigate a product's physical and functional characteristics. It may also be used to put customer samples to the test. The following are the notable advantages of acceptance sampling:

• Inspection expenditures are reduced by lowering the number of objects examined.
• Production schedules are more flexible since fewer products must be examined during the approach.
• It reduces inspection time for each item since fewer items are checked simultaneously.
• It may be used for practically any product or service.
• It does not need extensive training.
• It assists producers in determining if their goods fulfill certain basic quality criteria.

What are the disadvantages of Acceptance Sampling?

Acceptance sampling is a well-rounded process with various applications; however, it still has a few drawbacks. The following are the notable disadvantages of acceptance sampling:

• Acceptance sampling needs to provide more information about how well your process performs.
• The samples are typically a small proportion of the total and may cause issues sometimes. For example, if someone selects 10 items from each of 100 boxes on a pallet, one may find that the first 10 pieces meet the requirements, but the other 90 do not. However, it is rare but possible. This means that the firm potentially wasted time and money on a lot of faulty products because the batch needed to test more units in it to provide quality assurance during its manufacturing cycle.
• Testing may be subjective and costly depending on how it is carried out (e.g., if someone needs training before performing tests properly).

When should acceptance sampling be used?

Acceptance sampling can be applied in a number of scenarios, including when:

• Choosing whether or not to create a batch of items
• Putting new production procedures and equipment to the test
• Checking to see if there are any problems with existing products
• Determining if a product meets requirements and standards
• Ensuring that an assembly process has been effectively performed
• Evaluating product samples before they are offered to customers

This method may be utilized in several settings. Still, it is most effective when several flaws can be detected with a single sample by following the same specified specifications. Acceptance sampling, for example, could also be used to determine whether all cereal boxes were made to the same specifications.

If all the boxes have similar characteristics, one will notice that each box has roughly the same cereal and sugar as the preceding box. If not, one will know which packets require more sugar before being sold.

Acceptance Sampling Examples

Example1

Assume someone has created a new line of flannel shirts to sell on Amazon. In that instance, they may start with an acceptance sample test. They might choose 100 customers at random, send them each a shirt from their new line, and ask them to review on Amazon.com about their experience with the item. Assume that only less than 10% of purchasers rate the garment less than four stars out of five (or any other rating system). This means that the availability of satisfied customers is high. In such a scenario, one may be certain that it meets the quality standards for sale on Amazon's marketplace.

Example 2

For example, suppose someone is producing 5,000 widgets and know that approximately 10 faulty units are created for every 1,000 units. In that case, the firm can build up a testing system in which just 100 devices are examined for each batch. Suppose the firm is very strict about the quality of the goods. If no defect is found in those 100 widgets, then the entire batch will be considered acceptable. However, if even a single defective device is found, the entire batch will be rejected. The acceptance and rejection limits are decided on the basis of the contract between the manufacturer and the firm.

Example 3

For example, suppose someone is making widgets and wants to check or ensure they're all precisely three inches long. In that case, he can acquire some of their finished devices and measure how many are near enough. If there is only one outlier (a widget larger than three inches), the manufacturing process is running properly.

If, on the other hand, there were ten outlier widgets among the twenty items selected for measurement, it is time to know that the manufacturing process needs some attention because it's most certainly producing far more than one faulty widget out of every twenty units manufactured.

What is the goal of Acceptance Sampling?

Acceptance sampling aims to limit the possibility of faulty parts being included in a final product. Companies may use this strategy to guarantee that only high-quality items are supplied to consumers, increasing the likelihood of repeat purchases.

Before beginning mass manufacturing or distribution, firms can use acceptance sampling to evaluate if their product fulfills their criteria. If it does not satisfy their requirements, they can reject the batch and begin over rather than continue manufacturing something of poor quality.

What distinguishes acceptance sampling from process control?

Process control is a prominent statistical strategy for monitoring and managing a process to create the desired output; hence, it is a process that is active throughout the manufacturing process, whereas sampling is done before or after the procedure to assess product quality.

The Bottom Line

Acceptance sampling has a wide range of applications, from production to retail. In general, acceptance sampling is performed to assess whether or not a product fulfills the quality criteria and meets the customer's requirements.