posting for ron.....

"I know someone will probably say this article might be in error itself.
But for most I believe it confirms the questionability of many studies
and the fact that a lot of people including some of our posters make
there decisions based upon possible flawed studies." Ron S

Link: jama.ama-assn.org/cgi/content/abstract/294/2/218

The article is posted by Dr. John Loannidis

==========

Contradicted and Initially Stronger Effects in Highly Cited Clinical
Research
John P. A. Ioannidis, MD
JAMA. 2005;294:218-228.

Context  Controversy and uncertainty ensue when the results of
clinical research on the effectiveness of interventions are subsequently
contradicted. Controversies are most prominent when high-impact research
is involved.

Objectives  To understand how frequently highly cited studies are
contradicted or find effects that are stronger than in other similar
studies and to discern whether specific characteristics are associated
with such refutation over time.
Design  All original clinical research studies published in 3 major
general clinical journals or high-impact-factor specialty journals in
1990-2003 and cited more than 1000 times in the literature were
examined.

Main Outcome Measure  The results of highly cited articles were
compared against subsequent studies of comparable or larger sample size
and similar or better controlled designs. The same analysis was also
performed comparatively for matched studies that were not so highly
cited.

Results  Of 49 highly cited original clinical research studies, 45
claimed that the intervention was effective. Of these, 7 (16%) were
contradicted by subsequent studies, 7 others (16%) had found effects
that were stronger than those of subsequent studies, 20 (44%) were
replicated, and 11 (24%) remained largely unchallenged. Five of 6
highly-cited nonrandomized studies had been contradicted or had found
stronger effects vs 9 of 39 randomized controlled trials (P = .008).
Among randomized trials, studies with contradicted or stronger effects
were smaller (P = .009) than replicated or unchallenged studies
although there was no statistically significant difference in their
early or overall citation impact. Matched control studies did not have a
significantly different share of refuted results than highly cited
studies, but they included more studies with "negative" results.
Conclusions  Contradiction and initially stronger effects are not
unusual in highly cited research of clinical interventions and their
outcomes. The extent to which high citations may provoke contradictions
and vice versa needs more study.

Controversies are most common with highly cited nonrandomized studies,
but even the most highly cited randomized trials may be challenged and
refuted over time, especially small ones.

Author Affiliations: Department of Hygiene and Epidemiology, University
of Ioannina School of Medicine, Ioannina, Greece, and the Institute for
Clinical Research and Health Policy Studies, Department of Medicine,
Tufts-New England Medical Center, Boston, Mass.

knowledge is power - growing old is mandatory - growing wise is optional    
"Many more men die with prostate cancer than of it. Growing old is
invariably fatal. Prostate cancer is only sometimes so."
http://community.webtv.net/PALMER_ENT/doc