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From: robison@eosp1.UUCP (Tobias D. Robison)
Newsgroups: net.ai
Subject: Re: Diagnosing strategies for humans?
Message-ID: <1247@eosp1.UUCP>
Date: Fri, 9-Nov-84 12:34:59 EST
Article-I.D.: eosp1.1247
Posted: Fri Nov  9 12:34:59 1984
Date-Received: Sat, 10-Nov-84 09:31:47 EST
References: <1339@pucc-h> <1180@eosp1.UUCP> <3102@utah-cs.UUCP> <15636@lanl.ARPA>
Reply-To: robison@eosp1.UUCP (Tobias D. Robison)
Organization: Exxon Office Systems, Princeton
Lines: 39
Summary: 

This is a followup on the discussion of how doctors reason when
doing diagnoses:

>I don't think it would alarm anyone who does deductive reasoning a lot.
>The method described IS deductive reasoning.  As Sherlock Holmes once 
>observed: 'when all that is impossible has been removed, whatever remains,
>no matter how improbable, must be the truth.'  This doesn't prevent checking
>out the most probable (or the most easily tested) first.

Sherlock Homes did not, in my opinion, describe what doctors do.
In the first place, many tests are available to doctors, some simple
and inexpensive, to rule out the improbable.  Usually these tests are
not performed until the more likely cases are checked out.  A good
example is a diseased gall bladder.  Its common symptoms are similar
(depending upon how people report them) to lower backpain, ulcers,
and other forms of gastric distress, including viruses.  Doctors
almost always will do the more painful, and more expensive ulcer test
first (barium X-ray), before checking for gall bladder disease, which
is less common.

Sherlock Holmes always reasoned on the basis of very little
information, but he was careful to collect all he could at a given
moment, and then was ready to deduce from that the ONLY possibility,
however improbable.  Doctors will collect some of the information
easily available to them, and then deduce the most probable cause,
no matter how many possible causes are still not ruled out.

Please recall that I'm not flaming about all this.  Anyone who has
suffered from one of the less likely possibilities will prefer that
more deductive reasoning were used sooner; but I can appreciate that
doctors have a system that works a high percentage of time, and also
minimizes the number of tests required, at the cost of delaying correct
treatment to arelatively few cases.  I'm not sure that any alternative
would be better.

	- Toby Robison (not Robinson!)
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