Interpretation summary for Demonstration Test Plan

Use demonstration test plans to determine the sample size or testing time needed to demonstrate, with some level of confidence, that the reliability exceeds a given standard.

The two types of demonstration tests are as follows:
  • Substantiation tests, which provide statistical evidence that a redesigned system has suppressed or significantly reduced a known cause of failure. You are testing the following:

    H0: The redesigned system is no different from the old system.

    H1: The redesigned system is better than the old system.

  • Reliability tests, which provide statistical basis that a reliability specification has been achieved. You are testing the following:

    H0: The system reliability is equal to a goal value.

    H1: The system reliability is greater than a goal value.

You can rewrite these hypotheses in terms of the scale (Weibull or exponential distributions) or location (other distributions), a percentile, the reliability at a particular time, or the mean time to failure (MTTF). For example, you can test whether or not the MTTF for a redesigned system is greater than the MTTF for the old system.

Minitab provides an m-failure test plan for substantiation and reliability testing. If more than m failures occur in an m-failure test, the test fails.

Data description

You have traced early transmission failures occurring on a track-type tractor to a specific ball bearing. The failure times for this ball bearing follow a Weibull distribution with a shape of 1.3 and scale of 1,000 hours. You have 3 redesigned units available for testing and must determine how long to test each unit using a 0-failure test plan.

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