JiscMail Logo
Email discussion lists for the UK Education and Research communities

Help for SPM Archives


SPM Archives

SPM Archives


SPM@JISCMAIL.AC.UK


View:

Message:

[

First

|

Previous

|

Next

|

Last

]

By Topic:

[

First

|

Previous

|

Next

|

Last

]

By Author:

[

First

|

Previous

|

Next

|

Last

]

Font:

Proportional Font

LISTSERV Archives

LISTSERV Archives

SPM Home

SPM Home

SPM  2004

SPM 2004

Options

Subscribe or Unsubscribe

Subscribe or Unsubscribe

Log In

Log In

Get Password

Get Password

Subject:

Re: accepting the null hypothsesis

From:

Paul Fletcher <[log in to unmask]>

Reply-To:

Paul Fletcher <[log in to unmask]>

Date:

Wed, 23 Jun 2004 10:48:48 +0100

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (189 lines)

Dear Stuart,

Thanks for this - my failure to respond is not through pique but, rather, I
was away on holiday..

I agree with much of what you say. One must of course be wary of assuming
that something like fMRI will identify differences in task-related activity
with the same degree of certitude that we can identify blackness in ravens.
A lack of difference in 12 fMRI subjects, or even, if it is a huge fMRI
study consisting of 16 or 20 subjects, would not be as weighty as finding
1000 black ravens. in the latter case, sheer numbers, plus a clear
understanding of what constitute raven-ness and blackness must instil
confidence. Therefore, I concede to you in principle but suggest caution in
practice when the independent variables are under-specified and the outcome
variables are noisy (and the n is relatively small). As you say, though,
replication or, at least, accumulation of consistent data cannot be ignored.
This is currently rare rare in functional imaging I think.

(Isn't there also a logical problem to be considered - i.e. all ravens are
black is the equivalent of all non-black things are non-ravens. Thus, every
time you find something white that isn't a raven, you've added evidence in
favour of your hypothesis. So every seagull that I saw on my holiday was in
fact a piece of evidence in favour of your view that all ravens are black.
Tee hee).

Thanks for the mail
Very best
Paul

----- Original Message -----
From: "Dr. Stuart WG Derbyshire" <[log in to unmask]>
To: <[log in to unmask]>; <[log in to unmask]>
Cc: <[log in to unmask]>
Sent: Thursday, June 10, 2004 10:45 PM
Subject: Re: accepting the null hypothsesis


Dear Paul et al:

At the risk of generating a thoroughly annoying debate let me state
that I believe finding 1000 black ravens is tremendously informative
if trying to prove that all ravens are black.

If it is my hypothesis that all ravens are black, discovering black
ravens is obviously supportive of that theory but it is also the
only evidence in favour of the hypothesis that I can possibly
uncover. Does it ever get more important and informative than this?

So I find my 1000 black ravens and report the finding to a reputable
journal. It is published and then you go out and find another 1000
black ravens and publish your findings. Two continents, 2000 black
ravens. Then our good friends and colleagues in Asia, not to be
outdone, hunt down a further 2000 black ravens. Their work, too, is
published in a fine journal and things are looking pretty good for
the "all ravens are black" hypothesis.

Then someone finds a white raven and it appears on the front cover
of Science. Darn it. So all ravens are not black then? Well, maybe.
Perhaps that raven fell into a bucket of white paint and was really
black all along. Or perhaps that raven is a dove looking a bit
ravenish?

Whatever Popper might have said, science does advance through an
accumulation of evidence that facilitates a growing consensus about
the natural world. Once we have developed an idea that fits the
evidence, and is predictive, we become highly skeptical of white
ravens popping up to spoil the story. This is not necessarily
because we are being dogmatic, though that can be the case, but it
is because we believe we are saying something important about the
character of ravens rather than about this peculiar white raven.

You can pelt me with raven poop in Budapest.

Stuart.


---- Begin Original Message ----

From: Paul Fletcher <[log in to unmask]>
Sent: Fri, 28 May 2004 08:45:09 +0100
To: [log in to unmask]
Subject: Re: accepting the null hypothsesis


Hello,

I would be a bit careful about making this the basis for an
experiment:
accepting the null hypothesis is avoided for very good reasons.
First, it is
an unsatisfying way to go about things - if you want to prove that
all
ravens are black (if this is your null hypothesis), finding one
white one is
far more informative than finding 1000 black ones. Second, the idea
of a
less stringent p value doesn't really help much. Imagine that you
set a p
value of 0.1 and found no difference - this would enable you to say
that,
even if you accepted a 1 in 10 chance of falsely rejecting the Null
hypothesis, you were unable to reject it. This isn't a very
convincing way
of saying that the null hypothesis is acceptable. If you increase the
threshold to p=0.5, you're giving yourself a 50% chance of falsely
rejecting
it. Still not a very compelling foundation for accepting it.

If I were you, I would try somehow to incorporate the
putative "sameness" of
the conditions into your design. I'm assuming that you believe them
to share
a process and that this sharing should be reflected in coincident
activation
in a given region (the region that does the process, if we want to
get
phrenological). One way of providing evidence that this is the case
would be
to compare the two conditions directly and to find no difference.
This would
be subject to the problems that you clearly recognise and that are
rehearsed
above. However, if each of them were compared separately to their own
control tasks (note: not to a common control task) and shown to
activate the
same region, then this would at least allow you to point to two
separate
null hypothesis rejections and to suggest on this basis, a shared
process
(assuming that there is a one-to-one mapping of process to region).
This is
akin to the position that Price and Friston put forward in advocating
conjunction analyses.

I don't think that this is watertight approach (for example, if you
want to
say that the two regions show the same magnitude of activation, it
becomes
more difficult) but it will perhaps allow you to formulate an
experiment
that is not dependent upon the dreaded acceptance of the null
hypothesis.

best wishes and good luck
Paul Fletcher

----- Original Message -----
 From: "Johannes Gerber" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, May 27, 2004 4:20 PM
Subject: [SPM] accepting the null hypothsesis


Hi,
a question: how would you design and analyse a functional imaging
experiment where you are interested in not rejecting the null
hypothesis.
that is, where you don't want to see a difference between two
conditions.
is there a great example in literature?

asking some knowledgeable people, there was the suggestion to lower
the
thresholds. but you always see something in SPM when lowering the
thresholds.... is there a more elegant way of doing it? I would be
happy
with any comment.

thanks in advance!

Johannes

Dr. med. Johannes Chr. Gerber
FA Diagnostische Radiologie
Abteilung Neuroradiologie
Institut und Poliklinik für Radiologische Diagnostik
Universitätsklinikum Dresden
D-01304 Dresden
Tel.: 0351-458 5227 / -2660
Fax.: 0351-458 4370


---- End Original Message ----



Sent by Medscape Mail: Free Portable E-mail for Professionals on the Move
http://www.medscape.com

Top of Message | Previous Page | Permalink

JiscMail Tools


RSS Feeds and Sharing


Advanced Options


Archives

April 2024
March 2024
February 2024
January 2024
December 2023
November 2023
October 2023
September 2023
August 2023
July 2023
June 2023
May 2023
April 2023
March 2023
February 2023
January 2023
December 2022
November 2022
October 2022
September 2022
August 2022
July 2022
June 2022
May 2022
April 2022
March 2022
February 2022
January 2022
December 2021
November 2021
October 2021
September 2021
August 2021
July 2021
June 2021
May 2021
April 2021
March 2021
February 2021
January 2021
December 2020
November 2020
October 2020
September 2020
August 2020
July 2020
June 2020
May 2020
April 2020
March 2020
February 2020
January 2020
December 2019
November 2019
October 2019
September 2019
August 2019
July 2019
June 2019
May 2019
April 2019
March 2019
February 2019
January 2019
December 2018
November 2018
October 2018
September 2018
August 2018
July 2018
June 2018
May 2018
April 2018
March 2018
February 2018
January 2018
December 2017
November 2017
October 2017
September 2017
August 2017
July 2017
June 2017
May 2017
April 2017
March 2017
February 2017
January 2017
December 2016
November 2016
October 2016
September 2016
August 2016
July 2016
June 2016
May 2016
April 2016
March 2016
February 2016
January 2016
December 2015
November 2015
October 2015
September 2015
August 2015
July 2015
June 2015
May 2015
April 2015
March 2015
February 2015
January 2015
December 2014
November 2014
October 2014
September 2014
August 2014
July 2014
June 2014
May 2014
April 2014
March 2014
February 2014
January 2014
December 2013
November 2013
October 2013
September 2013
August 2013
July 2013
June 2013
May 2013
April 2013
March 2013
February 2013
January 2013
December 2012
November 2012
October 2012
September 2012
August 2012
July 2012
June 2012
May 2012
April 2012
March 2012
February 2012
January 2012
December 2011
November 2011
October 2011
September 2011
August 2011
July 2011
June 2011
May 2011
April 2011
March 2011
February 2011
January 2011
December 2010
November 2010
October 2010
September 2010
August 2010
July 2010
June 2010
May 2010
April 2010
March 2010
February 2010
January 2010
December 2009
November 2009
October 2009
September 2009
August 2009
July 2009
June 2009
May 2009
April 2009
March 2009
February 2009
January 2009
December 2008
November 2008
October 2008
September 2008
August 2008
July 2008
June 2008
May 2008
April 2008
March 2008
February 2008
January 2008
December 2007
November 2007
October 2007
September 2007
August 2007
July 2007
June 2007
May 2007
April 2007
March 2007
February 2007
January 2007
2006
2005
2004
2003
2002
2001
2000
1999
1998


JiscMail is a Jisc service.

View our service policies at https://www.jiscmail.ac.uk/policyandsecurity/ and Jisc's privacy policy at https://www.jisc.ac.uk/website/privacy-notice

For help and support help@jisc.ac.uk

Secured by F-Secure Anti-Virus CataList Email List Search Powered by the LISTSERV Email List Manager