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8. Assessing Product Reliability
8.1. Introduction


What are some common difficulties with reliability data and how are they overcome?

The Paradox of Reliability Analysis: The more reliable a product is, the harder it is to get the failure data needed to "prove" it is reliable!

There are two closely related problems that are typical with reliability data and not common with most other forms of statistical data. These are: 

  • Censoring (when the observation period ends, not all units have failed - some are survivors)
  • Lack of Failures (if there is too much censoring, even though a large number of units may be under observation, the information in the data is limited due to the lack of actual failures)
These problems cause considerable practical difficulty when planning reliability assessment tests and analyzing failure data. Some solutions are discussed in the next two sections. Typically, the solutions involve making additional assumptions and using complicated models.
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