Nov-2009

A bias is a bias is a bias

By Dietmar StöcklSTT Consulting

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A bias …

VIM 4.20 (5.25)#

instrumental bias =

average of replicate indications minus a reference quantity value

… is a bias is a biashttp://en.wikipedia.org/wiki/Rose_is_a_rose_is_a_rose_is_a_rose

#http://www.bipm.org/en/publications/guides/vim.html

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Bias – Past & Present

There was (1) and there is (2) a tendency to put bias under the square root.

This was and this is wrong (3)!

This is NOT GUM!

When you HAVE a bias, TREAT it as a bias!

1 Harris EK. Arch Pathol Lab Med 1988;112:416-20.2 http://www.westgard.com/rilibak-2.htm3 Thienpont LM. Clin Chem 2008;54:1587-8.

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Treatment of bias

4 possibilities

─neglect it (when small)

─correct it

─report it

─put it into total error calculations(in principle, this is the same as "report it")

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Bias & GUM#

GUM unequivocally states that bias has to be corrected. Only in EXCEPTIONAL cases (F.2.4.5), bias may be REPORTED, but not taken under the square root.

In principle, we then come to the same numbers as the total error concept, just the other way round:TE = Bias + z x s; GUM = k x s + Bias.

The example given in GUM, however, does not exactly cover the situation in the clinical laboratory. Therefore, there always will be a point of discussion there.

#http://www.bipm.org/utils/common/documents/jcgm/JCGM_100_2008_E.pdf

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Nature of bias & Consequences thereof

Bias is a location measure, it will offset your whole population.

If you fail to recognize that as analytical chemist, you will do a bad job.

Accreditation, regulation, are other things. You should resist them when they ask you to do the wrong things.

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In the end

Media bias