Dear Sportsci reader,
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Senior Lecturer (Level C) in Biomechanics
School of Health and Human Performance
Faculty of Arts, Health and Sciences
CQU Rockhampton
Full Time, Tenurable
Closing date for applications: 17th November, 2004.
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School research interests include physical activity and it's role in health
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Peter Reaburn PhD
Head of School
School of Health and Human Performance
Central Queensland University
Rockhampton Q. 4702
Ph: (07) 4930 9813
Fax: (07) 4930 6875
E-mail: p.reaburn@...http://www.ahs.cqu.edu.au/hhp/index.htm
"A University should be a tributary to the real world, not a sanctuary from it"
I had the wrong link in my previous message. Alan actually sent me the
handbook, not the link. I got the link off Google and put it into his
message, but it was the wrong one. The correct link is
http://www.cochrane.org/resources/handbook/index.htm
Will
On October 21 I sent a request for help with meta-analysis of randomized
controlled trials. Specifically, I wondered whether using only the
post-test means and SDs in the experimental and control groups was an
appropriate way to estimate the effect and its standard error (and hence
its weighting factor in the meta-analysis), and I wondered whether this method
of analysis was being used to get around the problem of missing p values
(especially "p>0.05", but also possibly "p<0.05").
Ed Winter didn't have an answer but made some useful comments. Alan
Batterham pretty-much resolved the issue by finding the Cochrane Handbook
at the Cochrane site and sending me the relevant section. Ian Shrier also
helped by sending my query to a Cochrane statistician. His reply was
useful, but there were a few misunderstandings. George Kelley was going to
help but I forstalled him by sending him Alan's reply, which he agreed
with. The relevant responses are below.
In summary, yes, you can use only the post-test data for the meta-analysis
instead of the pre and post. Doing so will lead to loss of precision when
the within-subject SD is less than the pure between-subject SD (the usual
situation for most of the measures we deal with in exercise and sport
science, in my experience) and better precision when the within is greater
than the between (the situation for some physiological measures). There
are some other issues relating to randomization and matched-pairs analysis,
which those who are interested can find below.
Will
From: "Winter, Edward M" <E.M.Winter@...>
This is not much help for your specific query but your request seems to
lend support for the quoting of actual p values not simply > or < one's
chosen significance value - which is usually less than or equal to 0.05.
In my role as a reviewer of manuscripts, I usually find myself asking
authors to do just this. It helps for instance to distinguish between p's
of 0.049 or 0.051 and lets the reader judge the practical significance of
outcomes - although calculations of effect sizes, confidence intervals or
the like would be preferable. That of course takes us into debates about
hypothesis testing about which I think you and I are well aware.
From: Alan Batterham <spsamb@...>
I believe they address this issue, in part, in the Cochrane Handbook
http://www.cochrane.org/archives/handbook.doc . Excerpt below on change
scores vs final outcome scores.
In some circumstances an analysis based on changes from baseline will be
more efficient and powerful than comparison of final values as it removes a
component of between person variability from the analysis. However,
calculation of a change score requires measurement of the outcome twice and
in practice may be less efficient for outcomes which are unstable or
difficult to measure precisely, where the measurement error may be larger
than true between person baseline variability…
In practice a reviewer is likely to discover that the trials included in a
review may include a mixture of change from baseline and final value
scores. However, mixing of outcomes is not a problem when it comes to
meta-analysis. There is no statistical reason why trials with change from
baseline outcomes should not be combined in a meta-analysis with trials
with final measurement outcomes... If the use of change scores does
increase precision, the studies presenting change scores will appropriately
be given higher weights in the analysis than they would have received if
final values had been used, as they will have smaller standard deviations.
My edited reply to Alan:
...Your message has prompted me to work out exactly what the standard error
is in the two situations. I've written the following for eventual posting
to the list and/or use elsewhere.
Let sd be the within-subject error, and SD be the true between-subject
SD. Let n be the number of subjects in the exptal group and n also in the
control group. Assume no individual responses to the treatment.
Using difference of change scores, the standard error is root(4sd^2/n).
Using post-test scores, the standard error is root(2(SD^2+sd^2)/n).
So the break-even point occurs when sd=SD. This point corresponds to a
reliability correlation of SD^2/(SD^2+sd^2) or 0.50.
As an important aside, if you use just the post-test data, the total sample
size (n+n) needs to be nearly 800 with the traditional approach to
sample-size estimation, for a smallest Cohen effect of 0.20. Many
physiological measures have sd similar to SD, not because we measure them
poorly, but simply because we are all made of the same stuff at a
physiological level, and the variation we see in physiological measures
between subjects is due partly or largely to real within-subject
variation. Those physiological variables might also be controlling
variables rather than controlled variables in homeostasis, so they are
naturally variable. It follows that studies using ~10-20 subjects for such
variables are grossly underpowered, whether you analyze them for difference
in the changes or differences in the post-test. You would need to
meta-analyze dozens of such studies to get acceptable precision for trivial
or small effects.
By the way, the sample size of 800 refers to 0.20 of the observed
between-subject standard deviation; that is, 0.20 of root(SD^2+sd^2). If
you make it 0.2SD, as some would argue, the sample size needs to be even
larger. Four times as large if sd=SD. In the case of physiological
variables where sd is "real", I think it's sensible to use 0.20 of the
observed standard deviation. After all, if we were all truly clones, SD
would approach zero and all Cohen effect sizes defined using only SD would
approach infinity.
...A further thought occurs to me. For those variables where the
within-subject variation is greater than the true between, at first sight
there would appear to be little point in including any pre-test when you do
a controlled trial. Why inflate your uncertainty? But we do like to
randomize in a balanced fashion, in case there is an interaction between
the pretest score and the effect of the treatment. Then I remembered some
simulations I did a few years ago, as a result of interacting with Greg
Atkinson... If you randomize to the two groups in the usual pair-wise
fashion on the basis of the pre-test score of the dependent variable, you
can perform a "matched-pairs" analysis that counteracts to some extent the
additional error that arises from the usual repeated-measures analysis. In
the simulations, I performed the matched pairs analysis in two ways, but
the one that matters is a paired t test between the groups for the
difference in the post-pre change. I just checked the outcomes of the
analyses, and I found that the matched-pairs analysis pretty-much
completely offsets the loss of precision you get from the usual
repeated-measures analysis of post-pre changes. There are only some subtle
differences that appear to be due to the degrees of freedom for the t
statistic. In other words, for a reasonable sample size of around 20 or
more, you can use the pretest value in your analysis and not get any
inflation of the confidence interval, provided you use the matched-pairs
approach to the analysis. This approach works only when SD<sd, as defined
in that previous email. Matched-pairs analysis produces wider confidence
intervals than standard repeated-measures when SD>sd.
When you report your finding from a matched-pairs analysis, you would still
have to show the exact p value for this approach to feed through into the
meta-analysis. No-one does matched-pairs analysis, and few report the
exact p value, so the whole thing is academic anyway...
Edited reply from Cochrane statistician, and my edited responses:
>Regarding your friend's query I can offer a few thoughts:
>
>1. To me, the query confusingly mixes two different issues - missing
>data and use of change-scores vs post-intervention measures. These two
>issues are related, but not as intimately as the email suggests.
I was so surprised by the notion of all that info in pretests being thrown
away in the meta-analysis, that I presumed there had to be a good reason,
and missing p values seemed to me to be the only good reason. I was partly
aware of the issue of better precision when the error of measurement is
large, which is why I stated "in general the sampling error will be much
larger than the error derived from the p value for the comparison of the
changes in the experimental and control groups". I was right with "in
general", but I might have erred a little with "much" larger. It depends
on the variable. For some physiological variables most of the
between-subject SD is due to the within-subject SD, and for these just
using the post-test scores would be better. But why measure them at all in
a pre-test?
>2. Phrasing the problem in terms of missing P values strikes me as
>misguided. First, P values should not be considered the main summary of
>a statistical analysis.
Of course not, but it's often all that many authors give. Please note that
I do not approve of p values. In fact, I refuse to include them in any
publication with my name on it.
>Second, for obtaining data for meta-analysis
>such as those considered here (i.e. of continuous data), P values are
>used as a last resort only when standard deviations cannot be obtained
>directly.
I think you mean standard error of the effect statistic, not standard
deviations. The SE is an SD, of course.
>In particular, when your friend says "But you need the p value (or
>better, the confidence limits) to work out the sampling error for the
>effect, which you convert to the weighting factor for the effect in the
>meta-analysis", I'd have put it as follows: the weight is obtained from
>the standard error (or the variance) of the effect estimate, which is
>usually best obtained from summary statistics such as standard
>deviations.
No, I think your emphasis on standard deviations is a little--dare I say
it--misguided. :)
>Sometimes these are not available and standard errors can be
>obtained from confidence intervals, T statistics or exact P values.
You should first try to get the standard error from confidence intervals, T
stats, or exact p values, before you use pre and/or post SDs. But if the
error of measurement is so large that you get better precision from only
the post SDs, then you use those.
>As a
>last resort, in-exact P values (such as P<0.05 or P>0.05) can be used to
>impute standard errors, although this is not necessarily better than
>imputing using results from other analyses or other studies in the
>meta-analysis.
>
>3. I've had a quick look at the methods section of the Boule paper in
>JAMA, and must say I don't recognise your colleague's concerns. The
>authors have chosen to focus on post-intervention differences in the
>outcomes they look at. This is a solid and reliable approach to
>meta-analysing results of randomized trials. They do not discuss missing
>P values, but quite reasonably estimate outcome standard deviations
>using baseline standard deviations.
That last sentence can't be right. They used post-intervention SDs to get
the SE. They used pre-intervention SDs to get the denominator for the
standardized (Cohen) effect size, if I remember correctly. Or if they
didn't, they should have, because the post-intervention SD in the
intervention group could be inflated by individual responses. I am at home
and don't have the paper in front of me, and I won't be in to work for
another three days because we have a local conference at a hotel. There is
also the issue of whether the denominator in the Cohen should be the
OBSERVED SD or the TRUE SD (free of measurement error). In my view, it
depends on whether the "error" is due to technical measurement error or
true day-to-day within-subject variation. But that's another story. Does
Cochrane go into this issue?
>4. I'm guessing your friend's main problem is that the authors look at
>post-intervention differencess, but that they might have looked at
>differences in changes-from-baseline. The standard error of a difference
>in change-scores will often be smaller than that of a difference in
>post-intervention scores (with corresponding smaller P values and bigger
>weights). This does not necessarily indicate the the use of changes is
>to be preferred.
Yes it does.
>One reason is that standard deviations of
>changes-from-baseline are often missing, and they need to be imputed
>(occasionally based on in-exact P values).
But that was precisely my point!
Accepting Applications for Masters Candidates in Exercise Science at
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and 3) Strength and Conditioning. A limited number of graduate research
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the second year. A limited number of out-of-state tuition waivers are
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Interested candidates should contact Dr. Charles Dumke and consult the
exercise science graduate programs website.
Application Procedures
All applicants for admission to the Graduate School must:
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non-deductible application processing fee,
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Last reminder for the Biostats Group to submit for ACSM Thematic Poster
session. Please email me to let me know you have sent in the abstract, and
then I will let ACSM know exactly who should be presenting at our session.
Ian Shrier MD, PhD, Dip Sport Med (FACSM)
Past-president, Canadian Academy of Sport Medicine
check out: www.casm-acms.org
Centre for Clinical Epidemiology and Community Studies
SMBD-Jewish General Hospital
3755 Cote Ste-Catherine Rd
Montreal, Qc H3T 1E2
Tel: 514-340-8222 ext 7563
Fax: 514-340-7564
Young Investigator Special Issue (YISI) 1 of the Journal of
Sports Science and Medicine is now available for you to access the
abstracts and the full articles in http and pdf formats. The JSSM family
is proud to start this new service to the Sport Science community and to
young researchers. The Young Investigator Special Issue followed
a normal peer-review process, except that there were no straight rejections
in the first phase of review. We advised the reviewers of the Young
Investigator Special Issue to proceed with constructive advice and
remarks for all manuscripts. This offered a great opportunity for the Young
Investigators to revise the manuscript, while at the same time contributing
to the learning process.
We are very happy that we achieved our goal in a very short time. The
JSSM Young Investigator Special Issue became ready one month before
the planned schedule. Many expert referees wrote us and offered their help.
Many other referees accepted our revision request immediately despite their
busy schedule. The support of the supervisors was also substantial. At
this point, we would like to thank all contributors to this first issue
of the Young Investigator Special of the JSSM.
In the future, we hope that we can attract even more participants to
share their knowledge with us, to write up their own work and to increase
their motivation and confidence.
Finally, we hope that the readers will accept this Young Investigator
Issue as a scientific source for research.
Enjoy it!
Young Investigator Special Issue Editor Mustafa Atalay, MD, MPH, PhD
YISI Guest Editors Eric Eils, PhD
Jukka A. Salmi, MSc, MPH
JOURNAL OF SPORTS SCIENCE AND MEDICINE, NOVEMBER 2004 - VOLUME 3,
RESEARCH ARTICLE The physiological responses of chronic heart failure patients to maximal
strength test and a balke incremental test.
Itamar Levinger, Roger Bronks, David V. Cody, Ian Linton and Allan
Davie
http://www20.uludag.edu.tr/%7Ehakan/sbtd/yisi/1/1/yisi1-1.htm
RESEARCH ARTICLE Muscular oxidatýve capacity in ovariectomized rats discussion on the
endurance performance of female athletes with sports-related-amenorrhea.
Takahiro Sasa, Koichi Sairyo, Naoyuki Yoshida, Makoto Ishikawa, Mari
Fukunaga and Natsuo Yasui
http://www20.uludag.edu.tr/%7Ehakan/sbtd/yisi/1/3/yisi1-3.htm
RESEARCH ARTICLE Perceived exertion as an exercise intensity indicator in chronic heart
failure patients on beta-blockers.
Itamar Levinger, Roger Bronks, David V. Cody, Ian Linton and Allan
Davie
http://www20.uludag.edu.tr/%7Ehakan/sbtd/yisi/1/4/yisi1-4.htm
I received another message on the effects of lacto-ovo-vegetarian diet on body
building. This is from someone identified by another subscriber as '"the
authority" on nutrition for vegetarian athletes in the US.'
Chris Forbes-Ewan
THIRD MESSAGE ON LACTO-OVO-VEGETARIAN DIET AND BODY BUILDING
Much of my response will be my opinion in interpreting the literature,
or should I say lack of the literature.
First, It is my opinion that a healthy vegetarian diet should be able
to adequately support the training of all athletes. It is true that the
short term studies tend to suggest that men following a vegetarian diet
tend to have lower testesterone but this is not translated into lower
performance or strength. I do not know of any source that can plot
testesterone levels against strength or performance and get the answer
that the higher your testosterone levels are the better. The issue is
also complexed by the fact that testosterone is both free and bound,
that its effect is influenced by receptors, and that many other growth
factors (including insulin, insulin-like growth hormone, and growth
hormone) influence muscle metabolism and growth.
In my opinion, I feel much of the low testosterone may be from a
combination of a diet that is too low in fat and cholesterol and too
high in fiber. What is not known is by what mechanism this happens (as
you said) and whether the body adapts after so long on a vegetarian
diet. There is a whole body of literature looking at low fat diets in
general and testosterone that might assist in the specific mechanism.
I am not sure what your diet is like so it is hard to go from here. I
would strive to eat a diet that is a little higher in fat (30-35%)
rather than 15-20 if that is an issue and watch that your carbohydrates
are a balance of whole grains and natural more simple carbs. By this I
mean, don't just eat whole-wheat pasta and fresh fruit but mix it up
with regular pasta, rice, juice and lower fiber fruits and veggies.
In response to Gavin's query about differences in standard deviations
(SDs)... I'll comment on Gavin's specific issues first, then discuss the
more general issue of substantial differences in SDs. I would love to hear
from others on this topic.
>Does anyone know if it is possible to find out if data from two groups are
>heterogenous just from reported means and SDs ?
Heterogeneity refers only to a substantial difference in the SDs, in my
understanding. If distributions are non-normal, heterogeneity could
perhaps also apply to skewness, kurtosis, and even higher-order "moments",
but let's not go there.
>I have a number of studies
>I am reviewing which seem to have very heterogenous variances (double the SD
>for example)...
For anyone who just arrived from another star system, the variance is the
SD squared. Statisticians work with variances, but what matters in the
real world is SDs.
>...and despite large between-group mean differences report no
>significant findings.
Small sample sizes, no doubt. What are the chances that the true
difference between the means is clinically or practically worthwhile or
substantial? That is the important question that an analysis via
statistical significance does not address properly. I've built these
chances into my spreadsheets.
>Most authors give subject numbers, group means, S.D.s, S.E.Ms, t-stats or P -
>values and I was wondering if from these I can do an equivalent to a
>Levene's test for heterogeneity of variance?
The Levene "test" (I hate that concept) for heterogeneity of variance needs
only the SDs and the number of observations each came from (or more
exactly, the degrees of freedom for each variance). It's not clear why you
want to test for differences in the SDs. In my view you should always use
the unequal-variances t statistic, or its equivalent in mixed modeling,
when you estimate differences in means, regardless of what the test for
unequal variances shows.
Like tests for normality, tests for unequal variances are not particularly
useful, for three reasons. First, what's the point anyway, if you are
going to use the unequal-variances t statistic? Secondly, if the sample
sizes are small, there can be substantial differences in the SDs, yet the
test will not show significance, and most researchers will conclude
mistakenly that "there is no difference". Thirdly, if the sample sizes are
large, there can be trivial differences in the SDs, yet the test can show
significance, and most researchers will mistakenly conclude "there is a
difference". What matters is HOW BIG the difference is in the SDs, and how
uncertain you are about the difference, expressed as confidence limits for
the true difference and the chances that the true difference is clinically
or practically important.
Ah yes, but how big is BIG, when it comes to differences in SDs? That's a
question that my colleagues and I have been asking for a few years. Our
default at the moment is a factor of 1.15 (or a 15% difference). That was
based on a consideration of sample size needed to quantify confidently a
difference or change in means. The sample size is proportional to the
square of the appropriate SD, so a difference in the SD equivalent to a
factor of 1.15 would result in a difference in sample size of 1.32
(32%). But that's pretty arbitrary, and anyway, sample size is not the
most important issue. What matters is the impact on individuals, not
researchers. So the rest of this message is about an attempt to come up
with a new way to decide on what's a substantial difference in an SD.
Let's start with the example I often use to explain magnitudes of
differences in means: IQs of men vs women. Let's forget about the fact
that women on average have a higher IQ, and whether or not the difference
is substantial. Instead, let's assume men and women have the same mean
IQ. What about their SDs? Apparently men have a larger SD than women. A
larger SD implies that there will be more extremes in IQ amongst men than
women: the real geniuses and real dummies tend to be guys. Let's make the
difference in SDs extreme. Now draw any gal at random. Then draw any
guy. The guy will either be a genius relative to the gal, or a dummy. So,
how big does the difference in SDs need to be before the guy is likely to
be substantially brighter or dumber than the gal, rather than very much
brighter or dumber? That's the question.
Let's define substantially using my version of Cohen's scale: 0-0.2 is
trivial, 0.2-0.6 is small, 0.6-1.2 is moderate, and >1.2 is large. Add the
negative values to this scale (-0.2 to -0.6 is small, etc.). You end up
with seven size categories. I've just devised a spreadsheet to show that
if you draw two people at random from the same population, the chances of
the difference between them falling into each category range from 11% to
20%, with all seven size categories adding up to 100%, of course. Now draw
the second person from a population with a bigger SD. The spreadsheet
shows that the chances of the difference between the two individuals
falling into each category change: chances of trivial, small and moderate
differences fall, chances of large differences rise. When the second SD is
a factor of 1.11 bigger than the first, the chances of trivial and small
differences fall by a factor of 1.10, chances of moderate differences fall
by 1.07, and chances of large differences rise by 1.13. Changes in the
chances or rate of something of this order (relative frequency or risk of
1.1) are arguably the smallest that matter or that are noticeable. So it
looks like I have made a case for the smallest change in an SD being a
factor of 1.11, but let's make it 1.1 or 10%. I've played around with the
spreadsheet in other ways and got pretty-much the same answer.
I may have gone down the wrong track somewhere here. Or there may be a
better way to come up with the smallest difference in SDs. Anyone else got
any ideas?
Will
Dear All,
Does anyone know if it is possible to find out if data from two groups are
heterogenous just from reported means and S.D.s ? I have a number of studies
I am reviewing which seem to have very heterogenous variances (double the SD
for example) and despite large between-group mean differences report no
significant findings.
Most authors give subject numbers, group means, S.D.s S.E.Ms, t-stats or P -
values and I was wondering if from these I can do and equivalent ot a
Levene's test for heterogeneity of variance? Such stats are not commonly
(well, never) reported in the literature.
Any help prior to ACSM submission date would be greatly appreciated.
Gavin Sandercock
Research Centre for Health Studies
Buckinghamshire Chilterns University College
Chalfont Campus
Newlands Park
Gorelands Lane
Chalfont St. Giles
Buckinghamshire
UK
HP8 4AD
Tel: 01494 522141
I'm getting more and more involved with meta-analyses, and I have a
question about the way one gropu has apparently dealt with
missing p values in their meta-analysis.
You get lots of missing p
values when you meta-analyze something, because most authors misguidedly
state no more than p>0.05 when the effect is non-significant.
But you need the p value (or better, the confidence limits) to work out the sampling error for the effect,
which you convert to the weighting factor for the effect in the
meta-analysis. When the effect is significant, often all the
authors state is p<0.05, but at least then you can use the data by
assuming p=0.05.
The meta-analysis and approach in question is by Boule et al in JAMA 286,
1218-1227, 2001. They analyzed controlled trials of the effect of
exercise on glucose regulation in diabetics. For the magnitude of
the effect, they used only the difference in the mean effect between
exercise and control groups in the post-intervention assay. This
approach would allow them to get a sampling error without any additional
information, but in general the sampling error will be much larger than
the error derived from the p value for the comparison of the changes in
the experimental and control groups. I contacted the corresponding
author about it, but he didn't know whether it was a specific and
Cochrane-approved strategy for dealing with missing p values. The
best he could do was point me to part of the Cochrane site
http://www.cc-ims.net/RevMan/ivnotes.htm,
and there is no explanation there. I have clicked all around the
site looking for more info, but to no avail. A link to a handbook
is still not active. I could also find no accessible links for
seeking more information from Cochrane mavens.
Ian Shrier, George Kelley, and others, you help would be much
appreciated.
Will
Will G Hopkins, PhD FACSM
Work +64 9 917 9793, Fax +64 9 917 9960
Home +64 9 376 0198, Cell +64 27 427 2518
Health Science/Sport and Recreation
Auckland University of Technology
Private Bag 92006, Auckland 1020, New Zealand
will@...
Statistics:
http://newstats.org
Sportscience: http://sportsci.org
---------------------------------
Be creative: break rules.
Dear David, Chris and all on the list:
The comparison of men and women's world record, and their
progression is fascinating, which is why I guess the data (good, bad
or indifferent) often ends up in Nature, why it appears so
frequently in the media and why we all talk about it so much.
I think it's worth noting that when the prediction of world record
trends includes estimates of VO2max, lactate threshold velocity,
anaerobic power and capacity and VO2 kinetics (Peronnet and Thibault
(1989) J. Appl. Physiol., 67, 453-465), the predictions are
remarkably accurate. These authors predicted running performance
from 100 m to the marathon, the results for males were as follows
(predicted and actual data for the year 2000):
Event: Predicted (actual) [%error]:
100 m: 9.74 s (9.79) [0.5]
200 m: 19.53 s (19.32) [1.1]
400 m: 43.44 s (43.18) [0.6]
800 m: 1:39.88 (1:41.11) [1.2]
1500 m: 3:25.45 (3:26.00) [0.3]
5000 m: 12:42.72 (12:39.36) [0.4]
10 000 m: 26:43.63 (26:22.77) [1.3]
Marathon: 2:05:23 (2:05:42) [0.2]
Of course, the limits of the physiological parameters in the model
are still unknown, and the authors assumed a near-linear improvement
in these parameters over time. We could make educated guesses based
on data to estimate where the limits lie for both genders
(particularly for O2 transport and utilisation), but that rather
takes the fun out of the issue doesn't it? I think a few quotes
best sum up my thoughts on these issues:
"My records will stand for a while. The 400 m will be a tough
one to break I wouldn't bet against it being broken in the next
decade…
The 200 m? Well, you could make a good bet that that person's
grandmother hasn't been born yet."
Michael Johnson
"The more restricted our society and work become, the more necessary
it will be to find some outlet for this craving for freedom. No one
can say, 'You must not run faster than this, or jump higher than
that.' The human spirit is indomitable."
Sir Roger Bannister
All the best
Mark
Mark Burnley PhD
Department of Sport and Exercise Science
Carwyn James Building
University of Wales, Aberystwyth
SY23 3FD
UK
This is what I sent to Chris yesterday.
David Bishop's commentary prompts my distribution to the group as a whole.
Professor Edward M Winter
The Centre for Sport and Exercise Science
Sheffield Hallam University
Collegiate Hall
Collegiate Crescent Campus
SHEFFIELD S10 2BP
Tel 0114 225 4333 (International +44 114 225 4333)
Fax 0114 225 4341 (International +44 114 225 4341)
e-mail e.m.winter@...
www.thecentreforsport.com
-----Original Message-----
From: Winter, Edward M
Sent: 18 October 2004 10:21
To: 'Forbes-Ewan, Chris'
Subject: RE: Male vs female running performance
Dear Chris
The manuscript by Tatem et al. was in the September 30 issue of Nature (Nature
431, page 525) with supplementary data and details
of the analyses on the Nature website.
The results suggested that women will run the same time for the 100 m in the
2156 Olympics. This suggestion is based on a linear
extrapolation of data which gives rise to two immediate questions: first, are
the data linear and second is extrapolation
warranted?
There is strong evidence that a linear model was appropriate although
exponential modelling would probably be biologically
preferable, but that extrapolation one and a half centuries hence might well not
be the wisest of forecasts. For instance,
further extrapolation of a linear model would reveal when men and women would be
running 100 m in zero time . . .
I wasn't sure if this manuscript was tongue-in-cheek, even a hoax, but it has
caused debate. It is similar to an earlier
manuscript from Nature by Whipp and Ward, quoted by Tatem et al., that women
would be running marathons in the same time as men by
about 2020.
Exponential modelling can perhaps be illustrated by the crossing-a-room
paradigm. Start at one wall and facing the opposite one
and move half way across. Then move to half the remainder i.e. to three quarters
of the way across, followed by half the remainder
again to seven-eighths and so on. You will always get closer to the opposite
wall but you will never actually reach it.
Time itself will tell whether or not the equality of performance forecasts are
accurate. For my part each projection is unlikely
but that shouldn't prevent debate about the relative influence on performance of
biological and cultural factors.
this article did catch my attention in nature a few weeks ago. While I question the authors' interpretation of the data, it does make one think about the possible limits of human performance, which I think is a good thing. However, questions undoubtedly arise when predictions are based solely on statistical trends and do not include constraints based on what has been learned from the sports sciences. There are inevitable limitations in assuming linear behaviour in improvements to a complex phenomenon such as human performance. Does anyone on the list really believe that the complex interaction between future changes in diet, training, drugs, equipment, surfaces and psychology (to name a few) can be explained by a simple linear relationship?
Even without scientific evidence to support their conclusions, I was surprised that the authors did not discuss the lack of success previous authors have had in predicting athletic performance. In a 1992 study by Whipp and Ward (cited by the authors), who also used linear extrapolation, it was stated that the “projected intersection (between male and female records) for the marathon is 1998” . By the end of 1998, the women’s world record for the marathon was still more than 10 minutes behind the men’s. In 2004, the world record marathon time for the men (2:04:55) remains more than 10 minutes faster than that for the women (2:15:25); although the gap has narrowed slightly.
It is probably less surprising that the authors did not extend their linear extrapolation to its logical (or illogical) conclusion. While there remains a lot that we don’t know about the human body, and it would be foolish to place limits on what the human body can do, it is difficult to believe that the current linear progression will continue indefinitely and we will see men completing the 100-m final in approximately zero seconds at the 246th Olympiad in 2876! It is also a shame that the authors did not investigate the linear progression (r2 of 0.93) in women’s pole vault records (since 1988). At the same time that current linear trends predict that women will run faster than men, we can predict that women will be pole vaulting over 14 m.
Just because the model fits, it doesn't mean that we should wear it!
David
David Bishop PhD MAAESS Lecturer - School of Human Movement & Exercise Science
Dr David Bishop
School of Human Movement & Exercise Science (M408)
The University of Western Australia
35 Stirling Highway
Crawley WA 6009
Ph: +61 8 6488 7282
fax: +61 8 6488 1039
"The University of Western Australia: CRICOS Provider No: 00126G"
I believed that the original Tatem paper was published in Nature. Just like
another paper published in Nature 4 years ago by S Savaglio and V Carbone
'Human performances: Scaling in athletic world records' Nature 404: 244,
2000, the Tatum paper is an example of non-sports science related
investigators playing an interesting, if poorly informed and executed, game
of 'what if'. Both papers defy common sense, ignore everything we know
about the limitations of human performance and, in my view, hamper the
efforts of serious investigators using modeling techniques to better
understand the determinants (and limits) of human muscular performance.
Granted that Nature doesn't publish very much in the sports science domain
(they have certainly rejected everything I have ever sent to them), if they
are willing to publish such ill-concieved pieces as the Tatem article, one
must wonder about the quality of the other science published in Nature.
Maybe they don't deserve their ~29 impact factor from ISI? While granting
that paradigm challenges, often from seemingly ill-prepared outsiders, are
the creative energy that drives revolutionary change in science, the dark
side of such glaring failures of the peer review process is a decrease in
the signal-to-noise ratio relative to really understanding our world.
Carl Foster, Ph.D.
Professor of Exercise and Sport Science
University of Wisconsin-La Crosse
I'm having trouble getting ahold of the following article.
Wilson, G.J. Disinhibition of the neural system: Uses in
programming, training, and competition. Strength and Conditioning
Coach 3(3): 3-5, 1995.
If anyone has it could you send me a copy even our library can
not get it on interlibrary loan.
Thanks
dan becque
--
M. Daniel Becque, Ph.D., FACSM
117 Davies Hall
Department of Physical Education
College of Education and Human Services
Southern Illinois University Carbondale
Carbondale, IL 62901-4310
mailto:mdbecque@...
Homepage at: http://exphys.siu.edu
618-453-3117 (office phone)
Biostats Group
Joe Weir asked the question below and I figured everyone would have the same
question. You should submit the abstract under Epidemiology. There is no way
to actually indicate that the abstract should be part of the thematic poster
session. The plan is for you to also inform me of the confirmation you
receive (title, etc), and I send the list to ACSM Program committee, and
then they will organize the abstracts into one session.
Hope this clears things up.
Ian Shrier
>-----Original Message-----
>From: Weir, Ph.D., Joseph [mailto:Joseph.Weir@...]
>Sent: 13-Oct-2004 3:37 PM
>To: Ian Shrier
>Subject: RE: ACSM 2005 Biostats Poster Session
>
>
>Ian - what sort of info does the abstract submission have to have in it
>in order to let ACSM know that the submission needs to go to the stats
>session?
>
>Joe
>
>Joseph P. Weir, Ph.D. FACSM
>Professor and Research Coordinator
>Division of Physical Therapy
>Des Moines University - Osteopathic Medical Center
>3200 Grand Avenue
>Des Moines, IA 50312
>515.271.1733
>FAX 515.271.1714
>joseph.weir@...
>www.dmu.edu
Howdy Chris,
I recommend contacting D. Enette Larson PhD, RD at the Pennington
Biomedical Research Center, Louisiana State University. Information on her
work:
http://www.pbrc.edu/facultyprofile.asp?links=research&EmployeeID=1396
Her e-mail is: larsonde@...
She is considered "the authority" on nutrition for vegetarian athletes
in the US.
Ellen Coleman, RD, MA, MPH
Sports dietitian
Biostats Group
Abstract deadline is less than 3 wks away and we need to firm up if there
will be Thematic Poster session. We asked about intentions before, and now
we need some committment. The following were the names and tentative
subjects. If you are on the list, please confirm that you still intend to
submit this. If you have an idea and are not on the list, please let us
know. It would be great to have as many as possible. One session would hold
5-6 abstracts, but who knows, maybe we can get two sessions!
Joe Weir: traditional tests for stationarity (runs test and reverse
arrangements) are not valid indices of stationarity in the frequency domain,
only the time domain
Joel Cramer: The purpose of the presentation would be a "validation" of the
continuous wavelet transform
Dwight The: 1) Fitting the four parameter Generalized Lambda Distribution
(GLD) to exercise science data: Learning what two parameter distributions
(e.g., the Normal) simply cannot tell us OR 2) Invoking different
statistical distributions to (Re)interpret the ACSM Guidelines' "Physical
Fitness Testing Norms"
Gavin Sandercock: Meta-analysis
Munish Chander: Sport injuries
Ian Shrier and Will Hopkins
Two years ago I wrote a review paper about the effects of vegetarian eating on
"Effect of Vegetarian Diets on Performance in Strength Sports". It was published
in Sportscience:
(Sportscience 6, sportsci.org/jour/0201/cf-e.htm, 2002).
I recently received a message about an aspect that wasn't addressed in the
review. If anyone would like to attempt an answer to the following question, I'd
be very pleased to forward the answer to the person who sent me the message:
"I have a question that I have been researching and finding minimal answers to.
I am a lacto-ovo vegetarian (no meat and no fish, but I eat eggs and milk),
steroid-free, novice bodybuilder. I have read in numerous books, magazines,
websites, academic papers (such as your own), etc. that vegetarians have lower
testosterone levels than meat-eaters. I have not found a reason why this is the
case. Could it be because in the studies that produce such results, the
vegetarians were not supplementing their diet with enough B-vitamins, zinc,
essential fatty acids, etc. or is there something else inherent in eating animal
flesh that raises one's testosterone level. You mention in your article,
"Deborah Shulman suggested that at least 12 weeks would be needed for studies
comparing the effects on performance at strength sports of nutrient-rich
vegetarian diets with those containing meat." Has a study like this been done in
the past 2 years, or do you think you know what the results woul!
d be? I have considered experimenting with adding meat to my diet for a trial
period simply to see if it has an effect on my bodybuilding and strength
training, despite having been a vegetarian for about 4 years. Do you think it
would be worth it to eat meat? Please tell me any thoughts you have on this
subject. Thanks."
Chris Forbes-Ewan
Defence Scientist (Nutrition) S&T 5
Defence Nutrition
DSTO-Scottsdale
PO Box 147
SCOTTSDALE Tas 7260
AUSTRALIA
Phone: Int + 61 3 6352 6607 (03 6352 6607 within Australia)
Fax: Int + 61 3 6352 3044 (03 6352 3044 within Australia)
The opinions expressed in this message are those of the author, and should not
be taken to represent the position of the Defence Science and Technology
Organisation or of the Australian Department of Defence.
IMPORTANT: This email message remains the property of the Australian Defence
Organisation and is subject to the jurisdiction of section 70 of the CRIMES ACT
1914. If you have received this email message in error, you are requested to
contact the author and delete the message.
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As a follow-up to the postings by Joe and Will, here is some information that may be useful for finding the "standard error of the mean predicted score" and the "standard error for an individual predicted score," which I refer to as SEMPS and SEIPS, respectively (for a lack of better acronyms).
Concept of the Standard Error of a Predicted Score (most of which is provided by Dr. Joe Weir):
Regarding the conceptual difference between SEMPS and SEIPS, Pedhazur (1997) states that "A predicted Y for a given X can be viewed as either an estimate of the mean of Y at the X value in question or as an estimate of Y for any given individual with such an X" (p. 203). Typically in the field of Exercise Science, Kinesiology, and/or Sports Medicine we are most interested in an individual's estimate of Y for their given value of X. Such is the case for any/all skinfold equations that attempt to estimate an individual's body density with multiple predictors, such as the sum of skinfolds, age, height, weight, etc. Therefore, the focus here is to find the standard errors for individual predicted scores (SEIPS) and calculate confidence intervals about the predicted score. What this means in practical terms is that a predicted value from a regression equation is not just a stand-alone value, since there is error associated with prediction equations. Therefore, what is usually done is that the standard error of estimate (SEE) is calculated for a regression equation, and an individual's response is denoted as Y +/- SEE. For example, Heyward (2002) points out that in ideal situations, the best SEE for a skinfold equation is roughly 3 - 5% body fat. Therefore, if someone is estimated at 20% body fat, we can be reasonably sure their body fat is somewhere between 15% and 25%. However, the SEE is only true for estimated values that are near the mean of the population from which the regression equation was derived. So, the standard error for an individual predicted score (SEIPS) will grow larger as the individual's body fat gets farther from the mean. In short, setting confidence intervals for predicted scores based on the SEE of a regression equation is only accurate when the predicted score falls exactly on the mean of the population from which the regression equation was derived. Any derivation from the mean will inflate the confidence intervals about the predicted score, beyond the SEE for that regression equation.
How to Obtain the Standard Error of a Predicted Score:
Pedhazur (Chapter 8, 1997 3rd ed, p. 195-207, referenced below) provides mathematical/algebraic equations for calculating the standard error of mean predicted scores (SEMPS) and the standard error of individual predicted scores (SEIPS), however, these equations pertain only to regression equations that incorporate one independent variable (i.e., one predictor; bivariate regression). On p. 206, Pedhazur (1997) describes an algebraic manipulation that allows for the calculation of SEIPS values for multiple regression equations, which is different from Pedhazur's 2nd ed (1982). The algebraic equation works well provided that one is able to obtain "leverage" values for various combinations of independent variable responses in the multiple regression equation. Leverage, in the world of regression, is an individual observation's undue influence on the regression equation that is analogous to a "lever" providing increased power to pull the regression line in one direction or another. Thus, leverage is a useful tool for identifying outliers, and in bivariate regression leverage is simple to calculate for any given value of the independent variable (see Pedhazur, 1997, p. 48). However, multiple regression (more than one predictor) falls under the mystique of multivariate statistics, which is based on matrices and matrix algebra. Therefore, the calculation of leverage for independent variable responses in multiple regression inherently involves matrix algebra. It may be useful to note that leverage is directly related to Mahalanobis distance, which is a well-known statistic for identifying multivariate outliers (leverage is actually a value located in the hat matrix). For more information on the relationship between leverage and Mahalanobis distance, see Tabachnick and Fidell (Using Multivariate Statistics, 4th ed, 2001, Allyn and Bacon, p. 68). In short, unless one is able to calculate leverage or Mahalanobis distance for independent variable responses in multiple regression with matrix algebra, obtaining SEIPS values algebraically for multiple regression equations is quite difficult (but probably not impossible).
For those who use SPSS (version 11.5), obtaining SEIPS values for multiple regression is relatively simple. For the "point and click" method, go to the ANALYZE menu --> Regression --> Linear... Once the dialog box for specifying the regression equation is visible, and after the regression equation is specified, click on the "Save" button. The dialog box that appears allows the user to specify "Prediction Intervals." There is a box for "mean prediction intervals" and "individual prediction intervals." There is also a box for specifying the level of confidence for the confidence intervals (the default is 95%). The SEIPS values are obtained by checking the "individual prediction intervals" box. SPSS then saves the new SEIPS values in the original data file (.sav). There will be two additional columns of values, one for the upper 95% confidence interval and one for the lower. In case you are wondering, I have tested these values based on the equations provided by Pedhazur (1997) and using the example data provided by Pedhazur (Table 8.1, p. 200), and everything works out nicely.
For those of you who prefer using the syntax method for SPSS, the following syntax will provide the SEIPS values:
REGRESSION
/DESCRIPTIVES MEAN STDDEV CORR SIG N
/MISSING LISTWISE
/STATISTICS COEFF OUTS R ANOVA CHANGE
/CRITERIA=PIN(.05) POUT(.10) CIN(95)
/NOORIGIN
/DEPENDENT y1
/METHOD=ENTER x1 x2
/SAVE ICIN .
Where, y1 = the dependent variable, and x1 and x2 are independent variables. The key to this syntax is the "/SAVE ICIN." This will save the SEIPS values to the original data file (.sav). If you play around with the SEIPS values, you will find that as an individual's predicted value deviates from the mean of the predicted values, the confidence interval grows exponentially.
References:
Heyward, V.H. Advanced Fitness Assessment and Exercise Prescription 4th ed. Human Kinetics, Champaign, IL. 2002.
I sent this to Joe Weir a few days ago, but it bounced back at me.
If anyone on the list is at Joe's institution, please let him know
something's wrong with his mail.
Gidday, Joe. I fear the problem will be intractable, because you
will need to take into account all the covariances among the
predictors. I checked to see whether Excel provides new-prediction
errors in its LINEST function, but alas it doesn't. The closest it
gets is the standard error of the estimate, which of course is the
prediction error only for the observations that produced the
prediction equation. A package like SAS provides new prediction
errors, but using matrix algebra. You get the prediction error for
any given new point by including the point in the data set, with a
missing value for the dependent variable. Output the predicteds and
there you will find the predicted value with its standard error. You
also get the standard error and confidence limits for the population
predicted value for that point.
Will
Has anybody exerienced any differences between HRs observerd during
an incremental test and during a steady state exercise bout for a
given sub-maximal work rate. Eg, HR during incremental test stage =
150bpm vs HR during 15min bout of work at the same intensity = 128
mean (135 max).
Any thoughts?
Rob
Dear List,
Forgive me if this request is inappropriate, however, I am searching for an owner's manual for a nordic track medalist plus ski machine. Anyone out there have one to copy for me. Thank you and apologies again if this is unwarranted.
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Clinical and Sport Psychology
AAASP, Certified Consultant
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I am looking for a Latin American expert to consult with coaches of
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This position is located within the
Exercise Metabolism research group, in the laboratory of Dr Glenn
McConell. The appointee will be involved in a project related to a
Cooperative Research Centre (CRC) Bushfire Grant in conjunction with the
Country Fire Authority (CFA). Dr McConell is contracted by the CFA
to conduct research as part of the CRC Bushfire Grant. The
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The appointed Postdoctoral fellow will be responsible for the design and
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health and fitness guidelines for safe fire fighting. The appointee
will be responsible for writing 3 monthly reports for the CFA and for
maintaining the budget for this consultancy. The appointee will
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reports suitable for distribution to Firefighting authorities. The successful applicant will be required to co-supervise an honour’s
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Experience with conduction of complex human exercise experiments.
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Evidence of independence in the conduct of research.
Excellent oral and written communication skills
Desirable
Self-motivated
Ability to work both as an individual and a team member
Ability to maintain accurate records of laboratory activities
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Well developed problem solving skills.
Computer literate in Microsoft Office and statistical software
packages
Glenn McConell PhD
Senior Lecturer
Department of Physiology
The University of Melbourne
Parkville 3010
Victoria
Australia
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I am a coach and a masters student, I am at present
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