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Publication date: 11/10/2021

Parametric Reliability Demonstration

Use the Demonstration Explorer for Parametric Reliability to determine the number of units to put on test for a reliability demonstration. Select DOE > Sample Size Explorers > Reliability > Parametric Reliability Demonstration. Explore the trade offs between time, significance, number of failures, and the number of units to test.

Demonstration Explorer for Parametric Reliability Options

Set study assumptions and explore sample sizes using the radio buttons, text boxes, and sliders. The curve updates as you make changes to the settings. Alternatively, change settings by dragging the cross hairs on the curve or adjusting the values in the axis text boxes.

Fixed Parameters


Specifies the probability of a type I error, which is the probability of rejecting the null hypothesis when it is true. It is commonly referred to as the significance level of the test. The default alpha level is 0.05.


Specifies the assumed failure time distribution. Distributions available are: Weibull and Lognormal. For more information about these distributions, see Statistical Details for the Life Distribution Platform in Reliability and Survival Methods.

Demonstration Time

Specifies the minimum length of time that an item under test should survive with the intended reliability.

Demonstration Reliability

Specifies the probability that an item under test survives until the defined Demonstration Time of the reliability standard

Scale parameter

Specifies the scale parameter for the failure time distribution.

Note: The Scale field is denoted Weibull β when the specified Distribution is Weibull.

Demonstration Parameters

Parameters that are inter-related and update as you make changes.

Maximum failures allowed

Specifies the maximum number of failures allowed for a successful test demonstration.

Sample Size

Specifies the total number of units on test needed for your demonstration.

Test Time

Specifies th length of the demonstration test in time.

Save Settings

Saves the current settings to the Saved Settings table. This enables you to save a set of alternative study plans. See Saved Settings in the Sample Size Explorers.

Make Data Collection Table

Creates a new data table that you can use for data collection.

Statistical Details for the Parametric Reliability Demonstration Explorer

For a parametric reliability demonstration test, the test time needed to demonstrate that the product achieves a demonstration time Td with reliability Rd is computed using a Binomial distribution with probability of success computed using the assumed lifetime distribution.

The test time for the Weibull distribution is computed as follows:

Equation shown here

The test time for the lognormal distribution is computed as follows:

Equation shown here


Equation shown here

Equation shown here

and c is the maximum number of failures allowed during the demonstration.

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