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# Sample number estimation

Before carrying out a product's minimum failure rate tests, qualifying the test that we want to carry out and deciding on the proper number of samples to be tested is recommended.
Ellistat offers several calculation methods:

## Guaranteeing a proportion of survivors for a cycle time

Ellistat facilitates the construction of reliability tests in order to guarantee a point on the reliability curve or a proportion of survivors for a given cycle time.
In order to do this, enter the desired test parameters in the first table. And choose the variable which you wish to calculate.
• Tested time: Corresponds to the cycle time that you want to guarantee
• Proportion of survivors: Corresponds to the minimum proportion of survivors produced during the tested cycle time that you want to guarantee.
• Parameter β: Estimate of parameter β on the failure curve. Refer to the paragraph "Main types of failures" to make an estimate of the Beta parameter.
• Degree of confidence: The degree of confidence you wish to guarantee for this proportion of survivors for this cycle time, generally 95% or 90%.
• Nb of products being tested: The number of products being tested.
• Test duration: The number of cycles that the products under testing will undergo.
• Number of failures: Estimate of the number of failures that will occur over the course of the test.

## Calculate a minimum testing time to ensure a MTTF:

Ellistat enables you to construct your reliability tests to guarantee an MTTF, i.e. the mean time to failure.
• Mean tested: Corresponds to the MTTF that you want to guarantee
• Parameter β: Estimate of parameter β on the failure curve. Refer to the paragraph "Main types of failures" to make an estimate of the Beta parameter.
• Degree of confidence: The degree of confidence you wish to guarantee for the given proportion of survivors for the given cycle time, generally 95% or 90%.
• Nb of products being tested: The number of products being tested.
• Test duration: The number of cycles that the products under testing will undergo.
• Number of failures: Estimate of the number of failures that will occur over the course of the test.

## Guaranteeing a survival rate by carrying out tests without failure:

Finally, Ellistat enables you to construct simple reliability tests in order to guarantee a rate of survival for a given number of cycles::
• Desired survival rate: Corresponds to the minimum survival rate for the tested duration that you want to guarantee.
• Degree of confidence: The degree of confidence you wish to guarantee for the given proportion of survivors for the given cycle time, generally 95% or 90%.
• Minimum size: To number of products that need to be tested to guarantee the given survival rate.

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