Defects

A defect is, basically, a failure to conform to requirements, in particular a non-conformance of a quality variable such as size, weight, etc.

Normally, defects are found against stated requirements, but anything which causes customer dissatisfaction can be regarded as a defect -- and possibly caused by an internal defect in the process by which customer needs are identified.

It has been said that most defects are, in fact, usability defects, which come from a design process that pays more attention to functionality than how people actually use the product in practice.

Defective

A 'defective' is an item, assembly or product which does not conform to requirements. A defective may contain one or more defects, so counting defects and counting defectives are quite different.

Defects Per Opportunity (DPO)

At any point in time there is opportunity for error or failure of some kind. DPO is a measure of how many defects occur within a given set of opportunities (which may be one or many). It is calculated simply as the number of defects divided by the number of opportunities.

Defects Per Million Opportunities (DPMO)

DPMO is a common metric used in Six Sigma. In production process, it is the average number of defects per unit identified during an average production run divided by the number of opportunities to make a defect during that run, normalized to one million. Mathematically, this is:

DPMO = (1 million X number of defects) / ( number of units X number of opportunities per unit).

The same principle may be used in other processes, for example a service process where the customer is touched many times and in many way.

A potential problem with DPMO is the accurate determination of what 'opportunities' means.

Defective parts per million (DPPM)

This is the number of defective items per million produced, where each item may contain multiple defects.

Defects per unit (DPU)