Hi all
What is/are correspondent's views on reportin sig figs to EQAS
Is reporting of different levels to EQAS regarded as cheating, because there
is no doubt that performance can be enhanced in the light of earlier
discussion, or should we report the EQAS results axactly as we would a
patient ?
My view is the latter but then I am one of the older F**ts of the profession
and am not sure whether I believe the next significant figure analytically
or clinically which is why I don't report it.
Perhaps the EQAS teams might have a view, since their result forms (Clin
Chem - Birmingham anyway) has what I would regard as insignificant figures
expected (not shaded out) eg Na(1), K(2), alb(1), urea(20, bili(1), prot(1)
And yet calcium (2), phos(2), Mg(2), and Trig(2) I would agree with
clinically
with best wishes
Richard
Richard Mainwaring-Burton
Consultant Biochemist
Queen Mary's Hospital
Sidcup, Kent
DA14 6LT
020-8308-3084
-----Original Message-----
From: Robin Marks [mailto:[log in to unmask]]
Sent: 01 December 2003 10:03
To: [log in to unmask]
Subject: Re: Significant Figures
Hello. Sorry for coming late into the Significant Figures discussion.
With regard to TSH result reporting, results such as 0.003 or 123.456 are
reported using a fixed format of 3 decimal places. The latter result gives
the impression to users that all 6 figures are significant.
We could (and probably should) report the result with an error estimate.
However, our computer systems are generally unable to handle this.
As a compromise, I wrote the following Basic code for formatting TSH (and
other) results:
DecimalPlaces = 0
for i = 0 to 2
If result/33 < 10^(-i) then DecimalPlaces = i + 1
next i
Here are some examples of results formatted using this code:
raw result reported result
345.911 346
033.911 34
032.911 32.9
003.391 3.4
003.291 3.29
000.339 0.34
000.329 0.329
000.034 0.034
000.003 0.003
We have been formatting TSH results in this way for about 15 years.
In summary, results over 33 are reported to the nearest whole number,
results less than 0.33 are reported to 3 decimal places, and results in
between are reported to give a last-digit error of between 1/33 and 1/330,
depending on the actual TSH result.
One could change the 33 in the algorithm to another number, say 50, giving a
'last digit error' of between 1/50 and 1/500.
Dr Robin Marks
Consultant Chemical Pathologist
Calderdale Royal Hospital
Halifax
HX3 0PW
UK
> -----Original Message-----
> From: Graham Jones [mailto:[log in to unmask]]
> Sent: 21 November 2003 6:32
> To: [log in to unmask]
> Subject: Re: Significant Figures
>
>
> Regarding the number of significant figures to which to
> report results,
>
> I agree with Roger Ekins that an analytical result SHOULD be
> reported with
> measurement uncertainty attached. I gather this has been
> tried many years
> ago in a Sydney laboratory, and I am sure in other locations,
> and was very
> poorly received by the clinicians. The increased complexity
> of the reports
> compared to the small amount of useful additional data for clinical
> decision-making provided by the added expression of
> uncertainty lead to its
> rapid abandonment.
>
> In general I would agree with Jonathan Middle's response about
> understanding the numbers, ie 123.4 indicates a number with implied
> analytical accuracy such that the result is likely to be
> between 123.35 and
> 123.45.
>
> The two problems I have with this are firstly the implied imprecision
> changes as the numbers change, for example a result of 1.1
> implies a CV of
> (1.15 - 1.05)/(4 x 1.1) = 2.2%; whereas the same number of significant
> figures at a different numerical value, eg 1.9, implies a different CV
> (1.95 - 1.85)/(4 x 1.9) = 1.3%.
>
> The second issue is the expression of significant figures with large
> numbers, eg does 12,300 mean 12,300 +/- 0.5; +/- 5 or +/- 50.
> There are
> ways to make this unambiguous (eg 1.23 x 10^4) but this again would be
> difficult for most laboratory computer systems as well as the
> receiving
> doctors.
>
> The paper referred to by Leslie Burnett is of interest in
> trying to address
> this issue. The authors (from the faded yellow pages on my top shelf)
> recognise the difficulty in obtaining the data for making the
> calculation.
> Some brief modelling shows that the number of decimal places
> (significant
> figures) changes within a decade. eg Modelling urea with an
> analyical CV of
> 2% and a within-person CV of 11%, values up to 6 mmol/L
> require 1 decimal
> place, but above 7 require no decimal places (model tests from 1 to 10
> mmol/L). This would be very difficult for most lab computer systems.
> Additionally I have a problem with setting 95% certainty levels
> arbitrarily, a clinician may be happy with 80% certainty for
> a clinical
> decision, and even the difference between 1 and 2 tailed
> probability (of
> there is an expected direction of change or not) will change
> the calculation.
>
> Also measurement of Lab CV should consider between-instrument CV if a
> patient may move between laboratories.
>
> So in the absence of a decent theoretical construct we need
> to rely on that
> lowly form of decision making: expert opinion. My two bobs
> worth would be
> as follows:
> Creatinine: report to the nearest 10 umol/L (0.01 mmol/L) for
> all results.
> Urea: report to the nearest 0.1 mmol/L up to 10 mmol/L then
> to the nearest
> 1 mmol/L.
> If your LIS can change the number of significant figures
> other than changes
> in decades other possibilities may be considered.
> Note that extra significant figures may be very useful for QC
> purposes.
>
> As this is my "expert opinion" I am sure there are many others. I look
> forward to hearing other ways of approaching this issue.
>
> Regards,
>
> Graham
>
>
>
> Dr Graham Jones
> Staff Specialist in Chemical Pathology
> St Vincent's Hospital, Sydney
> Ph: (02) 8382-9160
> Fax: (02) 8382-2489
>
>
>
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