In the former case the following are examples of reduction by
elimination: The impetus of Aristotelian
Physics, the
angelic motors of medieval celestial mechanics, the four
humors of ancient and medieval medicine,
demonic possession
as an explanation of mental illness, phlogiston theory from
premodern chemistry, and vital spirits of premodern biology.
In the latter case there are three examples from the history of
science where the simpler of two competing theories each of which
explains all the observed phenomena has been chosen over its
ontologically bloated competitor: the
Copernican
heliocentric model of celestial
mechanics over the Ptolemaic geocentric model, the
mechanical theory of heat over the Caloric
theory, and the Einsteinian theory of
electromagnetism over the luminiferous aether theory.
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Source - http://www.answers.com/Occam's%20Razor
Also, independently of statistical likelihood, some
patients do in fact turn out to have multiple diseases, which by
common sense nullifies the approach of insisting to explain any
given collection of symptoms with one disease. These misgivings
emerge from simple probability theory, which is already taken into
account in many modern variations of the razor; and from the fact
that the loss
function is much greater in medicine than in most
of general science, namely loss of a person's health and
potentially life, and thus it is better to test and pursue all
reasonable theories even if there is some theory that appears the
most likely.
Diagnostic parsimony and the counter-balance it finds
in Hickam's dictum have very important implications in medical
practice. Any set of symptoms could be indicative of a range of
possible diseases and disease combinations; though at no point is a
diagnosis rejected or accepted just on the basis of one disease
appearing more likely than another, the continuous flow of
hypothesis formulation, testing and modification benefits greatly
from estimates regarding which diseases (or sets of diseases) are
relatively more likely to be responsible for a set of symptoms,
given the patient's environment, habits, medical history and so on.
For example, if a hypothetical patient's immediately apparent
symptoms include fatigue and cirrhosis and they test
negative for Hepatitis C, their doctor might
formulate a working hypothesis that the cirrhosis was caused by
their drinking problem, and then seek
symptoms and perform tests to formulate and rule out hypotheses as
to what has been causing the fatigue; but if the doctor were to
further discover that the patient's breath inexplicably smells of
garlic and they are suffering from pulmonary edema, they might
decide to test for the relatively rare condition of Selenium poisoning.
Prior to effective anti-retroviral therapy for
HIV it was frequently stated
that the most obvious implication of Occam's razor, that of cutting
down the number of postulated diseases to a minimum, does not apply
to patients with AIDS - as they frequently did
have multiple infectious processes going on at the same time. While
the probability of multiple diseases being higher certainly reduces
the degree to which this kind of analysis is useful, it does not go
all the way to invalidating it altogether - even in such a patient,
it would make more sense to first test a theory postulating three
diseases to be the cause of the symptoms than a theory postulating
seven. <<<
Source - http://www.answers.com/Occam's%20Razor