Why: Conducting analysis of the early test results, when only a few failures have occurred, will give precursors as to passing/failing the longer term tests. If the early test results look encouraging, the larger test may be allowed to run to conclusion. However if early test results are disappointing, the test may be abandoned without using all of the testing budget so that remedial action can occur prior to completing the full scale planned test.
When: This testing is usually conducted prior to release of products. However, a similar watch may be setup for warranty repairs so as to anticipate the cost and extra supplies required to cope with an unexpected failure which was not forecasted.
Where: This strategy is appropriate for inexpensive components in the test laboratory. However, for warranty problems, the issues are very appropriate for expensive components or assemblies.
These definitions are written by H. Paul Barringer and are also posted on his web site at www.barringer1.com