Training and consultancy for testing laboratories.

Archive for the ‘Measurement uncertainty’ Category

Confidence intervals- How many measurements should you take?

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Confidence intervals – how many measurements to take

The concept of measurement uncertainty – a new perspective

Since the publication of the newly revised ISO/IEC 17025:2017, measurement uncertainty evaluation has expanded its coverage to include sampling uncertainty as well because ISO has recognized that sampling uncertainty can be a serious factor in the final test result obtained from a given sample ……

The concept of measurement uncertainty – a new pespective

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A linear regression approach to check bias between methods – Part II

 

Plot of reference and trial methods

A Worked Example

Suppose that we determined the amount of uranium contents in 14 stream water samples by a well-established laboratory method and a newly-developed hand-held rapid field method…..

A linear regression approach to bias between methods – Part II

A linear regression approach to check bias between methods – Part I

Plot of reference and trial methods

Linear regression is used to establish a relationship between two variables. In analytical chemistry, linear regression is commonly used in the construction of calibration curve for analytical instruments in, for example, gas and liquid chromatographic and many other spectrophotometric analyses….

A linear regression approach to bias between methods – Part I

 

 

Estimation of bias between two sampling methods

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Measurement uncertainty has two main contributors, namely sampling uncertainty and analytical uncertainty, but most laboratory analysts tend to equate analytical uncertainty as its measurement uncertainty based on the sample received.  This may be true when the target (population) lot sampled is homogeneous where every part of the target have an equal chance of being incorporated in the sample…..

Estimation of bias between 2 sampling methods

 

A worked example to estimate sampling precision & measurement uncertainty

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Nearly all analysis requires the taking of a sample, a procedure which itself introduces uncertainty into the final test result.  Hence a measurement uncertainty should cover both the uncertainties of sampling and analysis….

A worked example to estimate sampling precision and MU

Sampling designs for uncertainty estimation

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Experimental sampling designs for uncertainty estimation

Notes on sampling in chemical measurement

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Notes on sampling in chemical measurement

Decision risks in conformance testing – Part IV

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Decision risks in conformance testing – Part IV

Decision risks in conformance testing – Part III

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Decision risks in conformance testing – Part III