From: turpin@cs.utexas.edu (Russell Turpin)
Newsgroups: sci.med
Subject: The null hypothesis  (was: Xanax)
Date: 12 Sep 1992 11:44:55 -0500
Organization: U Texas Dept of Computer Sciences, Austin TX
NNTP-Posting-Host: cs.utexas.edu
Summary: No, in science it is *not* assumed.  But thinking so
	 is less important than practicing good medicine.

-*----
In article <1992Sep10.211606.7486@cbnews.cb.att.com> jap@cbnews.cb.att.com (james.a.parker) writes:
>> This is true [that someone making a claim has the burden of 
>> evincing it]; however readers should note that it is equally
>> true if the claims are that the cure is ineffective as well 
>> as effective.

In article <16446@pitt.UUCP> geb@dsl.pitt.edu (gordon e. banks) writes:
> In science, the null hypothesis is assumed. ...

I have to disagree with our inestimable neurologist.  From a
purely scientific viewpoint, I think he is wrong, though for
medical practice, it does not make that much difference.  (I will
explain this below.)

> ... It is up to those who claim the null hypothesis is false
> to prove it so. ...

In science, it is up to those who make *any* claim to prove it.

The issues here can be subtle.  There are two distinctions that
tend to get blurred.  The first is the distinction between
(1) asserting the negation of a claim, (2) *not* asserting the 
claim, and (3) asserting that the evidence for a claim is weak. 
In science -- indeed, in any field requiring careful thought --
these must be distinguished.

The second distinction is between the practical implications of
knowledge for (A) scientific discourse, and (B) medical practice.
In scientific discourse, the issue is: What can we empirically
know?  Lacking good evidence for a claim, we do not accept it.
But neither do we accept its negation until we have evidence for
*it*.  Most claims lie in the nether region where we can assert
neither them nor their negation.  Is there life elsewhere in the
universe?  Does some tropical plant hold a cure for cancer?  Are
there magnetic monopoles?  We do not know.  Many people shy away
from such blunt ignorance, but *that* is precisely the nature of
science.  If some quack asserts on poor evidence that a
particular diffusion of some orchid's leaves is a cancer cure,
the scientist may blast the evidence, and justly say the claim is
bogus, but the scientist may not legitimately say that the treatment 
is ineffective until there is evidence for *that* claim. 

But in medical practice, the issue is how to best maintain
health.  The medical practitioner has an obligation to only use
treatments for which there is some *positive* evidence of efficacy.
It is medically unethical (except, perhaps, in an experimental
setting) to use treatments merely because they are not proved
ineffective.  As many have pointed out, this weak claim applies
to almost everything.  We do not know that painting yourself blue
is ineffective against stomach ulcers, but that does NOT justify
prescribing it.  To recommend a treatment, a medical practitioner
should have some *reason* to think it will be useful. 

All this tends to get blurred because the niceties of scientific
discourse are often less important than fighting quackery.  If
someone is painting people blue to cure their ulcers, the
practical and ethical physician may say:

	It's ineffective, and this charlatan should be run
	out of town on a rail.

When challenged by some nitpicker in sci.med because there is no
proof that blue paint *doesn't* cure ulcers, it is then tempting
to respond that in science, the null hypothesis is assumed.
Unfortunately, this is not very good science.  A better response
would be:

	There is *no* reason to think that painting people blue 
	will cure their ulcers, and given this, it is unethical
	for a medical practitioner to use this treatment.

The quack should still be run out of town on a rail.  And it is
far more important for a practicing physician to display medical
ethics than it is for the physician to be oh-so-precise in 
discussing epistemology.  But since this *is* a newsgroup on
Internet, there is nothing wrong with picking a few of these nits
here. 

Russell
Newsgroups: sci.med