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Calculations with Insufficient Data

Minimum Data Requirements for Weibull++

Requirements for ALTA

The following sections describe the minimum data requirements for using different folios in ALTA. This includes:

Standard Folios

The minimum data requirements for ALTA standard folios are broken down by model in the table below. Note the following:

Life-Stress Model Give β or σ and Solve Exponential Weibull/Lognormal
Arrhenius/Eyring/Inverse Power Law

Failures = 2
Stress Levels = 2

Note: If you provide 3 or more failures at only 1 stress level, you can provide the acceleration factor to calculate.

Failures ≥ 2

Stress Levels ≥ 2

Failures ≥ 3
Stress Levels ≥ 2.

Temperature-Humidity/Temperature-Nonthermal

Failures = 3
Stress Levels = 3

Failures ≥ 3
Stress Levels ≥ 3

Failures ≥ 4
Stress Levels ≥ 3

Generalized Eyring

Failures = 4
Stress Levels = 4

Failures ≥ 4
Stress Levels ≥ 4

Failures ≥ 5
Stress Levels ≥ 4

Proportional Hazards/General Log-Linear

Failures = stresses + 1
Stress Levels = stresses + 1

Failures ≥ stresses + 1
Stress Levels ≥ stresses + 1

Failures ≥ stresses + 2
Stress Levels ≥ stresses + 1

Note: The lognormal distribution is not available for proportional hazards.

Cumulative Damage

Failures = stresses + 1
Stress Levels = stresses

Failures ≥ stresses + 1
Stress Levels ≥ stresses

Failures ≥ stresses + 2
Stress Levels ≥ stresses

Note: Only one stress column can be used with the lognormal distribution.

 

If you enter no data at all and click the Calculate icon, ALTA will prompt you to enter the values of the parameters for the selected model, as shown next. The appearance of the Parameter Input window will vary depending on the life-stress model and distribution selected.

Specify values for the parameters based on the selected life-stress model and distribution and click OK. All options and calculations supported by ALTA will be available except calculations involving confidence bounds and plots that require individual stress levels.

Degradation Analysis Folios

The minimum data requirements for degradation analysis folios are as follows:

 

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