Hi
The way I (simplistically) look at this issue is to consider the implied uncertainty of the measurement.
If you have a creatine result of 127 micromol/L, this implies that you can state with confidence that the result lies between 126.5 and 127.5 micromol/L. If 0.5 micromol/L therefore represents 2 SDs of the repeat measurement imprecision, 1 SD is 0.25 micromol/L, so the CV is 0.25/127 x 100 = about 0.2% (if this is the only source of uncertainty)!
If your uncertainty is nearer 2%, then rounding up to the nearest 10 (ie 130) is probably more appropriate. If your uncertainty is 20% then 'about 100' is probably all you can say.
By making this response I probably open myself up to a deluge of criticism from statistical quality control experts, but I hope this is helpful!
Cheers
Jonathan Middle
-----Original Message-----
From: "Beilby, John" <[log in to unmask]>
To: [log in to unmask]
Date: Wed, 19 Nov 2003 18:19:05 +0800
Subject: Significant figures
Dear All
We have recently had considerable discussion concerning the number of
significant figures that should be used in reporting biochemistry results.
Many laboratories in Western Australia report serum creatinine results in
umol/L, while other parts of Australia report in mmol/L.
It has been suggested that if we are going to use umol/L units we should
only report to the nearest 10 umol/L. I am interested in how other labs
deal with this problem as we cannot find much in the literature except for a
letter by Badrick and Hickman in Ann Clin Biochem 2002;39:162.
If we adopt the argument in this letter how many significant figures should
be used to report glucose and urea results, for example.
John
Dr John Beilby
Senior Biochemist
Clinical Biochemistry
PathCentre
Locked Bag 2009
Nedlands
Western Australia 6009
Tel 61 8 9346 2368 Fax: 61 8 9346 3882
[log in to unmask]
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