 |
 |
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 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> <HTML> <HEAD> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> <META NAME="Generator" CONTENT="MS Exchange Server version 5.5.2652.35"> <TITLE>AW: Significant change</TITLE> </HEAD> <BODY> <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>