Zusammenfassung
Randomized controlled clinical trials are conducted to determine whether
differences of clinical importance exist between selected treatment
regimens. When statistical analysis of the study data finds a P value
greater than 5\%, it is convention to deem the assessed difference
nonsignificant. Just because convention dictates that such study
findings be termed nonsignificant, or negative, however, it does
not necessarily follow that the study found nothing of clinical importance.
Subject samples used in controlled trials tend to be too small. The
studies therefore lack the necessary power to detect real, and clinically
worthwhile, differences in treatment. Freiman et al. found that only
30\% of a sample of 71 trials published in the New England Journal
of Medicine in 1978-79 with a P value greater than 10\% were large
enough to have a 90\% chance of detecting even a 50\% difference
in the effectiveness of the treatments being compared, and they found
no improvement in a similar sample of trials published in 1988. It
is therefore wrong and unwise to interpret so many negative trials
as providing evidence of the ineffectiveness of new treatments. One
must instead seriously question whether the absence of evidence is
a valid justification for inaction. Efforts must be made to look
for quantification of an association rather than just a P value,
especially when the risks under investigation are small. The authors
cite a recent trial comparing octreotide and sclerotherapy in patients
with variceal bleeding, as well as the overview of clinical trials
evaluating fibrinolytic treatment for preventing reinfarction after
acute myocardial infarction as examples.
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