At 2001-12-12 16:46 +0000, Trevor Tickner wrote:
>There is a problem with the traditional concept of 'diagnosis'.

Indeed! Let me tell a story from evaluation of a new method for diagnosis 
of AMI. We compared the current enzymatic method for CKMB with two new 
methods measuring CKMB-mass.

In the first study the department of cardiology reorganized and therefore 
the study was performed "double blind" i.e. we did not know anything of the 
clinical situation and the cardiologists evaluated the clinical records 
retrospectively without knowledge of the results of the new method. The 
patiens were judged strictly scientifically in three groups: "Obvious AMI", 
"suspect AMI", and "no AMI".

In the second study (another mass method) the records were not judged 
scientifically, but instead the diagosis in the computerized hospital 
diagnosis system was used.

In both studies the enzymatic method was performed for all patients. 
Therefore we could confirm that the selection of patients in the first and 
the second study did not differ.

However, the distribution of diagnoses in the computerized hospital system 
differed significantly from that of a scientific judgement. There was a 
considerable bias where the hospital system a significantly higher rate of 
"Obvious AMI".

This means that a great deal of the diagnoses in the hospital system were 
falsely positive with respect to AMI.

Obviously, there is a bias in health statistics because patients seeking 
care are more prone to get a false positive diagnosis than a false 
negative. On the other side, there are a lot of people having a disease but 
NOT seeking care, but they never appear in any health statistics!

When judging a diagostic method we must be very aware of this bias and 
therefore it is VERY important not to rely on routine diagnostic methods 
but to use the BEST scientific methods available for the comparison.

Mr Sten Öhman, PhD