Defects and defectives

In This Topic

What are defects and defectives?
A comparison of defects and defectives
Analyses for defects and defectives data

What are defects and defectives?

Customers expect products and services to meet their specifications. When they don't, a defect or defective is present.

Defects

A defect is any item or service that exhibits a departure from specifications. A defect does not necessarily mean that the product or service cannot be used. A defect indicates only that the product result is not entirely as intended.

Suppose service in a restaurant is being evaluated. If a waiter greets his table after 5 minutes, the customer can still order and enjoy a meal even though the promptness of the greeting did not meet expectations. Therefore, this could be considered a defect (“late greeting”) in the service.

Defectives

A defective is an item or service that is considered completely unacceptable for use. Each item or service experience is either considered defective or not—there are only two choices.

Before final shipment, a quality inspector evaluates auto supply parts and rates each item as “pass” or “fail” to ensure that the company does not ship any parts that will be unusable.

A comparison of defects and defectives

A defective item contains one or more defects. However, not all items with defects are defective. It depends on the severity of the defect. New cars may have several defects, some of which may not even be noticed by the customer. However, if the car contains a defect that is measured and reported, the car (or part of the car) may be considered defective.

Consider the loan application process. In this case, the processing department is the customer. You want to know how many defects they see. Your form has 36 entries. You sample 50 forms to estimate the defect rate. One application has 7 incorrect entries—there are 7 defects present on this form. Another application has 4 incorrect entries—there are 4 defects present on this form.

Overall, 18 forms have at least one defect, so 18 forms are defective out of 50. Overall, there were 62 total defects per 1800 opportunities (36 opportunities per form * 50 forms).

Analyses for defects and defectives data

The type of statistical analysis that you use depends on whether you are evaluating defects or defectives:

To evaluate defectives, you use analyses that are based on a binomial probability model, such as a 1 Proportion test, a 2 Proportions test, a P chart, an NP chart, or a binomial capability analysis. These analyses evaluate the proportion of defectives in your process.
To evaluate defects, you use analyses that are based on a Poisson probability model, such as a 1-Sample Poisson rate test, a 2-Sample Poisson rate test, a C chart, a U chart, or a Poisson capability analysis. These analyses evaluate the rate of defects in your process.

Note

The term "nonconformity" is sometimes used to signify a defect. The term "nonconforming" is sometimes used to signify a defective.