What is Effective Degrees of Freedom Formula
Short answer: The effective degrees of freedom formula is the Welch-Satterthwaite formula given in section G.4.1 of the JCGM 100:2008: νeff = uc4(y) / Σ[ui4(y) / νi]
coverage factor
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What is effective degrees of freedom
Short answer: Effective degrees of freedom (υeff) is an approximation of the degrees of freedom associated with the combined standard uncertainty. It is calculated using the Welch-Satterthwaite formula and used to quantify the reliability of the combined uncertainty estimate. According the JCGM 100:2008, it is calculated with the Welch-Satterthwaite formula and used with the Student’s […]
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How to determine coverage factor k
Short Answer: Determine the coverage factor k using JCGM 100:2008 Table G.1 (normal distribution) for uncertainties that meet the conditions of the Central Limit Theorem and JCGM 100:2008 Table G.2 (t-distribution) when the conditions are not met. Methods for Determining the Coverage Factor k According the the JCGM 100:2008 (GUM) Appendix G, there are […]
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What is a coverage factor (k)
Short Answer: A coverage factor is a multiplier that is used to expand measurement uncertainty to a desired level of confidence (e.g. 95 %). Coverage Factor Definition per the VIM According to the JCGM 200:2012 (VIM – Vocabulary in Metrology), a coverage factor is a “number larger than one which a combined standard measurement […]
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Why are some uncertainties assumed to be normally distributed while others are not
Short Answer: Some uncertainties are assumed to be normally distributed based on: Observations from the statistical evaluation of data, Information associated with the measurement uncertainty, Expertise with specific uncertainties, evaluation techniques, and data types, or Recommendations from the GUM, methods, guidance, and regulatory documents. If a normal distribution is not appropriate, then another probability distribution […]
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What is Expanded Uncertainty
Short answer: The product of multiplying the combined standard measurement uncertainty (uc) multiplied by a coverage factor (k). According to the Vocabulary in Metrology (VIM), expanded measurement uncertainty is “the product of a combined standard measurement uncertainty and a factor larger than the number one.” (Source: JCGM 200:2012, 2.35) Measurement uncertainty is commonly expressed in […]
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How to Calculate Expanded Uncertainty
Short answer: Multiply the combined standard measurement uncertainty (uc) by a coverage factor (k), where U = k x uc ISO/IEC 17025 accredited laboratories and ISO 17034 accredited producers calculate expanded uncertainty to a 95 % confidence interval where the coverage factor is two. The expanded uncertainty represents the interval y ± U which the […]
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