I had not come across David Burgess' formula either. I do know of the one which
takes analytical and within patient variation into account.
regards,
Martin.
Dr M R Holland
Dept Clinical Chemistry
New Cross Hospital
Wolverhampton.
____________________Reply Separator____________________
Subject: AW: Significant change
Author: "Auch Dieter" <[log in to unmask]>
Date: 30/11/00 09:17
In Tietz Textbook of Clinical Chemistry 3rd ed. p288 the formula for the 95%
confindence interval of a true change is:
(x1-x2) +/- 2 * root[sqr(sd1)+sqr(sd2)]
(x1-x2) +/- 2 * sd * root[2]
i.e. +/- 2.7 times standard deviation!
Or did I get it wrong?
Dieter
[log in to unmask]
Dr. med. Dieter Auch
Inst. f. Klin. Chemie und Pathobiochemie
Gaffkystr. 11
D-35392 Gießen
Tel: +49 641 99 41552
Fax: +49 641 99 41569
-----Ursprüngliche Nachricht-----
Von: [log in to unmask] [mailto:[log in to unmask]]
Gesendet: Donnerstag, 30. November 2000 04:29
An: [log in to unmask]
Betreff: Significant change
I'd like to share the contents of a memo from our principal scientist to the
director of pathology about what can be regarded as a significant change in
glycated Hb results. I do so of course with his permission - I think it's a
clear statement of analytical goals.
Gary,
The basic statistical rule for interpreting serial trends is:
There is a 95% probability that there is a real change if the difference
between
the two results is greater than 2.7 times the long term assay standard
deviation. This SD will vary with concentration - so you need to know the
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<P><FONT SIZE=2>In Tietz Textbook of Clinical Chemistry 3rd ed. p288 the formula
for the 95% confindence interval of a true change is:</FONT>
</P>
<P><FONT SIZE=2>(x1-x2) +/- 2 * root[sqr(sd1)+sqr(sd2)]</FONT>
<BR><FONT SIZE=2>(x1-x2) +/- 2 * sd * root[2]</FONT>
</P>
<P><FONT SIZE=2>i.e. +/- 2.7 times standard deviation!</FONT>
<BR><FONT SIZE=2>Or did I get it wrong?</FONT>
</P>
<P><FONT SIZE=2>Dieter</FONT>
</P>
<BR>
<P><FONT SIZE=2>[log in to unmask]</FONT>
<BR><FONT SIZE=2>Dr. med. Dieter Auch</FONT>
<BR><FONT SIZE=2>Inst. f. Klin. Chemie und Pathobiochemie</FONT>
<BR><FONT SIZE=2>Gaffkystr. 11</FONT>
<BR><FONT SIZE=2>D-35392 Gießen</FONT>
<BR><FONT SIZE=2>Tel: +49 641 99 41552</FONT>
<BR><FONT SIZE=2>Fax: +49 641 99 41569</FONT>
<BR><FONT SIZE=2> </FONT>
</P>
<P><FONT SIZE=2>-----Ursprüngliche Nachricht-----</FONT>
<BR><FONT SIZE=2>Von: [log in to unmask] [<A
HREF="mailto:[log in to unmask]">mailto:[log in to unmask]</A>]</FONT>
<BR><FONT SIZE=2>Gesendet: Donnerstag, 30. November 2000 04:29</FONT>
<BR><FONT SIZE=2>An: [log in to unmask]</FONT>
<BR><FONT SIZE=2>Betreff: Significant change</FONT>
</P>
<BR>
<P><FONT SIZE=2>I'd like to share the contents of a memo from our principal
scientist to the</FONT>
<BR><FONT SIZE=2>director of pathology about what can be regarded as a
significant change in</FONT>
<BR><FONT SIZE=2>glycated Hb results. I do so of course with his
permission - I think it's a</FONT>
<BR><FONT SIZE=2>clear statement of analytical goals.</FONT>
</P>
<BR>
<P><FONT SIZE=2>Gary,</FONT>
</P>
<P><FONT SIZE=2>The basic statistical rule for interpreting serial trends
is:</FONT>
</P>
<P><FONT SIZE=2>There is a 95% probability that there is a real change if the
difference between</FONT>
<BR><FONT SIZE=2>the two results is greater than 2.7 times the long term assay
standard</FONT>
<BR><FONT SIZE=2>deviation. This SD will vary with concentration - so you need
to know the</FONT>
</P>
</BODY>
</HTML>
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