Acceptance Sampling, Producer’s Risk(α), Consumer’s Risk (β) & Acceptable Quality Level (AQL)

Acceptance Sampling

Acceptance sampling is concerned with inspection and decision making regarding the entire lot/production/shipment

• A form of inspection used to accept or reject whole lot based on sample information

• Not consistent with TQM or Zero Defects philosophy

• Producer & customer agree on the number of acceptable defects

• A means of identifying not preventing poor quality

Application of Acceptance Sampling

A company receives a shipment of product from a vendor

- A sample is taken from the shipment, & quality characteristic of the products in the sample is inspected
- Based on data, decision is made either to accept or reject the entire shipment

The decision to accept or reject the shipment is based on the following set standards

Lot size = N, Sample size = n, Acceptance number = c, Defective items = d

If d <= c, accept lot & d > c, reject lot

Advantages of Acceptance Sampling

• It is usually less expensive because there is less inspection

• There is less handling of the product, hence reduced damage

• It is applicable to destructive testing

• Fewer personnel are involved in inspection activities

• It often greatly reduces the amount of inspection error

• The rejection of entire lots are opposed to the sample return of defectives often provides a stronger motivation to the vendor for quality improvements

Disadvantages of Acceptance Sampling

• Always a risk of accepting “bad” lots & rejecting “good” lots

• Less information is generated about the product or the process that manufactured the product

• Requires planning & documentation of the acceptance sampling procedure – 100% inspection does not

Risks of Acceptance Sampling

• Producer’s Risk(α)

- Refers to the probability of rejecting a good lot
- Also refered as Type ‘I’ error

• Consumer’s Risk (β)

- Refers to the probability of accepting a bad lot
- Also refered to as Type ‘II’ error

• Acceptable Quality Level (AQL)

- The numerical definition of a ‘good lot’.
- The percentage level of defective or nonconforming items at which the customer is willing to accept a lot as good.

• Lot Tolerance Percentage Defective (LTPD)

- Numerical definition of a ‘bad lot’
- Upper limit on the percentage defectives that a customer is willing to accept