Frequently Asked Questions About Quality

Please contact Media Sciences if your questions are not answered on these pages.

What is a test plan, and how do you define critical, major, and minor defects?

A test plan is an important part of any product specification. Although specifications may clearly define product quality requirements, expectations of the buyer and the vendor may be very different without a test plan that enables both parties to have a common perception of the required level of product quality.

In the absence of a test plan, an unrealistic buyer may expect zero defects while shoddy manufacturers may sample only a few parameters and accept as high as 5% or 10% failures. A test plan clearly defines what tests are to be performed, the sampling frequency and number of samples for each test, defect limits for each test, and accept/reject criteria for the product. It provides a clear path for enforcement of the specification without placing an unreasonable burden on the vendor.

Media Sciences recommends a broad test plan encompassing many types of tests performed on a limited number of samples. A few tests performed on large numbers of samples often fails to detect severe problems until field failures occur. Test results exceeding limits may be ranked as CRITICAL, MAJOR, or MINOR defects. Products may be rejected upon the occurrence of one or more test samples containing critical defects or two or more samples having major defects.

CRITICAL DEFECTS are severe flaws that are expected to cause unpredictable interchange failures. Upon their occurrence, use of the product should be discontinued until effective corrective action has been confirmed. Product recall may also be necessary.

MAJOR DEFECTS reflect serious interchange risks. Either enhanced quality monitoring should be used while prompt corrective action is taken, or product usage should be halted.

MINOR DEFECTS indicate significant, but marginal, flaws. They may arise from test failures that are within the error tolerances of equipment, but should have been prevented through use of guard banding by the manufacturer. Product usage may continue while corrective action is taken by the manufacturer.

A good test plan documents agreement between the buyer and the vendor on the level of product quality, provides for enforcement, properly ranks defects, details accept/reject levels for each defect, and encourages constructive corrective action when defects occur. The end result of a good test plan is improved quality, lower cost, and integration of vendors into your quality team.