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Re: Evidence

From: <dirk.colaert@agfa.com>
Date: Wed, 13 Jun 2007 09:42:19 +0200
To: Waclaw.Marcin.Kusnierczyk@idi.ntnu.no
Cc: public-semweb-lifesci@w3.org, public-semweb-lifesci-request@w3.org, Daniel Rubin <rubin@med.stanford.edu>
Message-ID: <OF7A478C2A.381F001E-ONC12572F9.0027FD34-C12572F9.002A5394@agfa.com>
I am following part of this thread and feel like popping in. Maybe it 

In clinical trials and 'evidence' based medicine the word evidence is 
strictly defined and may not be compatible with the word 'evidence' used 
in logic: if <evidence> then <conclusion>.
I support the idea of connecting the interpretation of the raw data (the 
source data) with the data itself. Pixels cannot be evidences on their 
own, without knowing what the pixels mean. So, an important fact is the 
thrust in the interpreter.

In Evidence Based Medicine (EBM) we use a classification of evidences, 
based on the source of the statement. If I, as an expert in the field, 
state "Aspirine is beneficial in the treatment of cardial ischemia in 70% 
of the cases" than this is considered as a statement with evidence class 4 
(the lowest). You have to take my world for it, you have to trust me.  If 
you do a randomized double blind clinical trial and you know (via 
statistical analysis) the sensitivity, the specificty and the confidence 
interval, the same statement is based on evidence class 1 (the highest). 

So, I think that in the definition of evidence you need to have more than 
the raw data. Raw data is in the 'real world' domain, evidence is a 
concept from the 'logic' domain. The interpretation of the raw data 
bridges that 'semantic' gap.

Summarizing I think that evidence
- is always about something (the statement)
- relies on the interpretation of raw data
- has a level, based on the thrust in the interpreter

We are using the concepts statement, interpretation, interpreter, raw 
data, level and thrust to describe something that we call "evidence".

Dr. Dirk Colaert MD
Advanced Clinical Application Research Manager
Agfa Healthcare               mobile: +32 497 470 871

Waclaw Kusnierczyk <Waclaw.Marcin.Kusnierczyk@idi.ntnu.no> 
Sent by: public-semweb-lifesci-request@w3.org
12/06/2007 21:27

Daniel Rubin <rubin@med.stanford.edu>
Re: Evidence

Daniel Rubin wrote:
> At 07:15 AM 6/11/2007, Matt Williams wrote:
>> I changed the subject line to make it more specific.
>> I think that Evidence is a tricky, slippery subject. It seems to be 
>> both traces (i.e. records of something) and in many cases, inferences. 
>> Those inferences probably shouldn't be called evidence, but they are 
>> the reason that some data are considered evidence, and others not, and 
>> hence often get included.
> Actually, sometimes the interpretation *is* part of the evidence--best 
> example is medical imaging wherein the radiologist interpretation of the 

> images are part of the primary evidence (the image is the "raw" 
> evidence, but you have no result without the radiology interpretation of 

> the image).

I'd think of the image as of a piece of evidence (of whatever the 
patient may suffer from), and the radiologist's interpretation (a 
written or spoken statement thereof) as another piece of evidence (of 
that the radiologist must have judged the image as a piece of evidence 
for whatever the patient may suffer from).  And the interpretation is 
only indirectly evidence for whatever the patient may suffer from, and 
only if we trust or otherwise know the qualifications of the 
radiologist.  If we doubt, the interpretation is no evidence;  and if we 
know the interpretation is wrong, it is evidence that the radiologist 
made a mistake (and perhaps is not a good one), but certainly not 
evidence that the patient suffers from this or that.

> Interpretation also transforms raw data into recoded variables that is 
> also used as evidence, for example in interpreting raw EKG tracings to 
> give the label of "ventricular tachycardia" or recording a sodium of 150 

> as "high sodium."

This is a similar case, though if we are based on firm rules (e.g., if X 
 > 10 then X is high), this recoding is hardly an interpretation, it is 
just a lossy translation from quantitative to qualitative form.

But both 'evidence' and 'interpretation' are terms used with many 
meanings, and perhaps instead of trying to answer the question 'what is 
evidence?' it is better to define the term:  'evidence', for our 
purposes, means ...

Received on Wednesday, 13 June 2007 07:42:35 UTC

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