Combined uncertainty factor for sampling and analysis

Ramsey, Michael H and Ellison, Stephen L R (2017) Combined uncertainty factor for sampling and analysis. Accreditation and Quality Assurance, 22 (4). pp. 187-189. ISSN 0949-1775

[img] PDF - Published Version
Available under License Creative Commons Attribution.

Download (733kB)


Measurement uncertainty that arises from primary sampling can be expressed as an uncertainty factor, which recognises its sometimes approximately log-normal probability distribution. By contrast, uncertainty arising from chemical analysis is usually expressed as relative uncertainty, based upon the assumptions of its approximately normal distribution. A new method is proposed that enables uncertainty from these two sources, expressed in these different ways, to be combined to produce an estimate of the total combined uncertainty of the measurement values that result when the measurement process is considered as a whole.

Item Type: Article
Additional Information: In the penultimate paragraph of the original publication, a confidence interval of 93 mg/kg to 971 mg/kg was reported. These values should be 114.5 mg/kg to 786.2 mg/kg. The intended exponent in the calculation was given as a multiplicative factor. The correct calculation is 300/1.619² to 300 × 1.619², since the expanded uncertainty factor is UF = (u′)ᵏ , in this case giving UF = (u′)² Official URL: - linked in 'Related URLs' below
Keywords: Measurement uncertainty Uncertainty factor Sampling uncertainty Propagation of uncertainty
Schools and Departments: School of Life Sciences > Evolution, Behaviour and Environment
Related URLs:
Depositing User: Michael Ramsey
Date Deposited: 30 May 2017 08:07
Last Modified: 02 Jul 2019 16:35

View download statistics for this item

📧 Request an update