May I interject a word of caution concerning "validated" evidence
hierarchies. Over the years we have from time to time looked into the
literature on the validity of evidence hierarchies. A related question, for
which there is more literature, and upon which the concept of evidence
hierarchies depends, is the question of the effect of study design on
research outcomes; i.e., whether double-blind RCTs are always necessary, or
whether in some situations more convenient study designs are adequate. In
general we have always found that the literature shows that the effect of
study design on research outcomes is topic specific. Because of this, the
search for a universally valid quality rating system appears to be futile.
When study design does not correlate with outcome differences, it may be for
one of two reasons. In some areas there is so much subjectivity, bias
(particularly publication bias) and fraud that the apparently best study
designs give results just as flawed as worse study designs. This may be the
case in some areas of pseudoscience where research is carried out by
proponents. On the other hand, in some research areas there are hard
outcomes, and conscientious researchers are sophisticated in research design
and data analysis, so that the better study designs may not improve
reliability over simpler designs. Some areas of cardiology come to mind
here. It is not uncommon in technology assessment to find RCTs that are
fatally flawed in terms of internal or external validity, and on the other
hand less rigorously controlled studies that are well done and reliable.
If study design does not invariably affect research outcomes, then it
follows that there can be no universal validation of evidence hierarchies
based on study design. In particular, whereas double-blind RCTs are in
general more reliable than less rigorous designs, the precise points
assigned to various study design aspects by a quality rating system are not
universally appropriate, and adjusting or weighting outcomes according to
such quality rating scores cannot be justified. Blind belief in these
rating scales applied to uncharted areas of research is simply not
A more reasonable approach is to use heterogeneity analysis to empirically
assess whether study design substantially affects outcomes in the particular
set of studies at hand. Heterogeneity analysis should not be merely an
inspection of heterogeneity test p values, because small sets of studies may
not have sufficient statistical power to detect clinically significant
differences in results. Regardless of p values, different study designs
that give results that appear to have clinically significant differences in
outcomes might best be grouped separately.
This is not a simple subject. Unfortunately going into our files and
putting together a comprehensive bibliography on this subject is beyond my
time constraints at the moment.
David L. Doggett, Ph.D.
Senior Medical Research Analyst
Health Technology Assessment and Information Services
ECRI, a non-profit health services research organization
5200 Butler Pike
Plymouth Meeting, Pennsylvania 19462, U.S.A.
Phone: (610) 825-6000 x5509
FAX: (610) 834-1275
e-mail: [log in to unmask]
From: Gero Langer [mailto:[log in to unmask]]
Sent: Monday, August 13, 2001 4:32 AM
To: [log in to unmask]
Subject: validated instruments for critical appraisal
I am looking for some validated instruments to critically appraise
studies. It is important to find the 'best' studies, and a (validated)
rating system for all kinds of questions (intervention, diagnosis,
qualitative etc.) should be used.
Currently I am using the JAMA users' guides, but they are not validated
(or?) and comparisons between studies are difficult and subjective. For
RCTs I am working with the Jadad score. With all of those I could get a
'result', but not a 'comparing' (e.g. rated) solution.
We are developing a database for nurses in Germany and trying to offer the
best available evidence for some nursing problems -- but what is unbiassed
the best? A scoring system would be very useful... Does anyone know of
anything in this field?
Thanks in advance,
Martin Luther University Halle-Wittenberg
Institute for Nursing and Health Sciences
German Center for Evidence-based Nursing
Website: www.EBN-Zentrum.de E-Mail: [log in to unmask]