Happy Thanksgiving, tipsters,
I think it is unfortunate that mind-over-matter mumbo jumbo has to be
employed in order to sell healthy lifestyle choices. I don't think for one
moment
that exercising and eating a reasonably healthy diet will cure cancer, but it
is well known that sedentary behaviors and high fat diets play a role in
raising the risk of certain cancers (breast and color among them). We should be
able to promote these strategies without the nonsense.
Since exercise is a known mood enhancer and stress reliever, it should be
recommended to those who have been diagnosed with cancer if they are physically
able to engage, for the same reasons. It can't hurt, and it may very well
help. If I was diagnosed tomorrow, I would hope that I could find the strength
and will to continue my exercise program even if in a more limited regimen. I
believe it would enhance my treatments to help me survive - not through
"magic" but through real physical benefit.
Nancy Melucci
Long Beach City College
Long Beach CA
Make a Small Loan, Make a Big Difference - Check out Kiva.org to Learn How!
In a message dated 11/27/2008 7:05:27 P.M. Pacific Standard Time,
[EMAIL PROTECTED] writes:
Stephen,
I don't know anything about Cox proportional hazards (except what I read in
Wikipedia). I do know, however, that chi-square is not a very powerful test,
and that it is is extra-lousy when the contignecy table it badly skewed, as
it is here (you did include the non-occurrences (of death), right?). That is
why it is conventional medical research (where most conditions are rare and,
therefore, most contingency tables are badly skewed) to use odd ratios. There
is no significance test I know of associated with odds ratios (but apparently
there isn't one associated with Cox either). In this case, the odds ratio
for cancer death would be:
25/88 .2841
-------- = --------- = 1.4205
19/95 .2000
which meas that you are 42% more likely to die of breast cancer without the
therapy, which sounds pretty important.
But the whole point of Gigerenzer et al's piece was that relative measures
of this sort can be misleading if the base rate is low, viz., that saying (if
I recall the numbers in his article correctly) that mammography cuts the risk
of breast cancer death by 33% sounds impressive, but when you tell people
that it means, say, 2 fewer deaths in a thousand cases (*before* you even
factor in the negative side effects of the procedure itself), they are
(rightly)
much less impressed.
In the research that concerns you, however, the authors are claiming about
5.5 fewer deaths per 100 ([25/113 - 19/114]*100), which is more worthy of
consideration that 2 in 1000, but is still not nearly the slam dunk that 42%
sounds like.
However, do not fret. I note that in their description of the aims of
therapy was included the phrase, "maintain adherence to cancer treatment."
Now, if
that was even partly accomplished by the therapy (that some people who would
have otherwise quit conventional medical treatment were persuaded to continue
to instead) then you have your answer without having to resort to spooky
mind-over-matter claims. It was the medical treatment that saved these extra
lives. What the therapy did was to ensure that a few extra people stayed with
their medical treatments.
Regards,
Chris
--
Christopher D. Green
Department of Psychology
York University
Toronto, ON M3J 1P3
Canada
416-736-2100 ex. 66164
[EMAIL PROTECTED] (mailto:[EMAIL PROTECTED])
_http://www.yorku.ca/christo/_ (http://www.yorku.ca/christo/)
==========================
[EMAIL PROTECTED] (mailto:[EMAIL PROTECTED]) wrote:
While indolent Americans are sleeping off their turkey comas, hard-
working Canadians, who would never indulge in such gormandising excess,
continue to think big thoughts on psychology. Here´s one.
It is widely believed, despite the absence of convincing evidence, that
cancer can be influenced by psychological factors, such as thinking
positive thoughts, having a healthful lifestyle, attending support
groups, or receiving therapy. This drives me nuts. It´s hard enough for
psychology to show any direct benefit from psychological intervention.
How much less likely that psychology can influence the course of a dread
disease with a clear biological basis. And this claim carries the
pernicious implication that if you´ve got cancer, it must be because
you´re doing something wrong.
Yet. A just-published study (Andersen et al, 2008) reports on the
progress of disease in women surgically treated for breast cancer and
continuing with medical treatment. They report that women additionally
exposed to 12 months of intensive group therapy, which included
"strategies to reduce stress, improve mood, alter health behaviours, and
maintain adherence to cancer treatment", produced significant long-term
benefits against their disease.
In particular, these women had "a reduced risk of breast cancer
recurrence...and [a reduced risk of] death from breast cancer". I´ve saved
the best for last. In contrast to our usual complaints about
correlational studies, this was a _randomized_ study, in which the
control group received assessment only. True, there was no placebo, but
I´m nevertheless gobsmacked that _anything _ like that, whatever it was,
could produce such a striking outcome. Even more remarkable, they also
reported "a reduced risk of death from all causes", which Gigerenzer
(2008, see comments below) considers the ultimate bottom line, one which
is rarely achieved. And the results were analyzed on an "intention to
treat" basis, which means that dropouts were counted as failures.
Do we therefore accept these exceptionally-encouraging conclusions? This
is where I bring in Gigerenzer (and you, gentle readers). There´s been a
lot of admiration expressed on this list lately for Gigerenzer et al
(2008), and justifiably. Their paper is clear and insightful and I´ve
learned a lot from it. I´ve been trying to use Gigerenzer´s ideas in
evaluating this paper, but I´m not sure I´ve got it right.
Gigerenzer recommends transparent framing of information, and recommends
that data be expressed as natural frequencies. The Andersen paper uses
"Cox proportional hazards analysis" (which is not transparent to me) in
an analysis of survival times. Gigerenzer criticizes the use of survival
time data and says it is uncorrelated with mortality, which he recommends
should be used instead. Yet his argument is based on the use of survival
times when methods of diagnosis differ (e.g. his Rudy Giuliani/prostate
cancer example). This is not the case here, as the groups are randomized
after receiving diagnosis by the same method, so any improvement in the
therapy group in survival time should be meaningful, and not subject to
this criticism .
But I´m concerned that while the analysis is for survival time and the
critical finding is displayed as a set of three graphs (Figure 3) of
recurrence-free survival time, breast cancer specific survival time, and
overall survival time, the language is frequently that of mortality (e.g.
the abstract claims "reduced...death from breast cancer [and]...from all
causes". I don´t see how they get from one to the other, and I wonder
whether this is just sloppy language for survival time data.
Then there´s this. Their Figure 2 provides all the data necessary at the
study end (median of 11 years follow-up) to do a natural frequency
analysis as recommended by Gigerenzer (but they don't). For the control
group (assessment only) 25 of 113 died of breast cancer; for the therapy
group, it was 19 of 114. For all causes of death, for the control, 30 of
113 died, while for the therapy group it was 24 of 114. Deaths in each
case are reduced by about 6% after therapy compared with control, which
seems meaningful (Hazard ratios around 0.8). But neither control vs
therapy comparison is even close to significance by a chi-square test
(e.g. Fisher´s exact), which means either there´s nothing there, or not
enough subjects were studied to show it.
So, what´s going on? Can Cox proportional hazards analysis demonstrate
something not evident by simple statistics? Are they justified in using
their mortality language when analyzing by survival times? Or are they
playing with statistics, and avoiding using an analysis which turns out
negative? My own feeling is that they should have explicitly carried out
the analysis I did, noted their failure to show an effect on mortality,
and discussed the implications for their Cox analysis. The press release
I have, BTW, prominently refers to the mortality claim, "The study also
found that patients receiving the intervention had less than half the
risk (44 percent) of death from breast cancer compared to those who did
not receive the intervention, and had a reduced risk of death from all
causes, not just cancer" (Science Daily, 2008/11/08). Not according to
my analysis of their data, though.
I would really like to hear from our statistics experts on this. The
abstract is here: _http://tinyurl.com/5z8fn2_ (http://tinyurl.com/5z8fn2) ,
although it would be better
to read the paper. If you don´t have access to it, I can supply a copy,
or you can get it direct from the author, who answered my request
promptly. She´s a psychologist at Ohio State University. Her address is
[EMAIL PROTECTED] (mailto:[EMAIL PROTECTED])
(As usual, I´m thinking about going the letter-to-the-editor route. But
I´m not sure I´ve got it right).
Stephen
Andersen, B. et al (2008). Psychological intervention improves survival
for breast cancer patients: a randomized clinical trial. _Cancer_, 113:
3450-8 [published on-line November 17, 2008].
Gigerenzer, G. et al (2008). Helping doctors and patients make sense of
health statistics. _Psychological Science in the Public Interest_, 8: 53-
96.
-----------------------------------------------------------------
Stephen L. Black, Ph.D.
Professor of Psychology, Emeritus
Bishop's University e-mail: [EMAIL PROTECTED]
(mailto:[EMAIL PROTECTED])
2600 College St.
Sherbrooke QC J1M 1Z7
Canada
Subscribe to discussion list (TIPS) for the teaching of
psychology at _http://flightline.highline.edu/sfrantz/tips/_
(http://flightline.highline.edu/sfrantz/tips/)
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