Hi Maria
I base my response on the asssumption that your clinical question is
addressing an issue of treatment ie a causal relationship. A sytematic
review or meta-analysis of studies other than randomised controlled trials
will never trump the evidence of a good randomised controlled trial (except
by chance). As you have demonstrated it is possible for both systematic
reviews and/or meta-analyses to include observational studies when pooling
results. However, it is well documented that observational studies predict
neither the direction of a treatment effect or the true size of the
treatment effect when compared to good randomised controlled trials. Even
systematic reviews of RCTs are fallible when faced off against really large
RCTs (the 1993 review on mag sulphate for MI is a good example when compared
to the ISIS-4 mega-trial)
The simple solution to your problem is to ignore the systematic reviews as
likely to introduce bias and random error into your answer (because of the
inclusion of observational evidence) and to take the RCT identified by
hopefully both reviews as the best level of evidence. That said, if the RCT
is a poorly designed, constructed or reported example, you still have
considerable uncertainty. But then that is the clinical world we live in -
we have to make decisions everyday in the face of imperfect knowledge. In my
view the role of evidence based practice is not to quantify certainty, but
to quantify uncertainty.
Regards
Andrew Jull RN MA(Appl)
Research Fellow
Clinical Trials Research Unit
School of Population Health
Tamaki Campus
University of Auckland
Private Bag 92019 Tel: +64 9 373-7599 Ext 84744
Auckland Fax: +64 9 373-1710
New Zealand Email: [log in to unmask]
-----Original Message-----
From: Olive Goddard [mailto:[log in to unmask]]
Sent: Friday, 1 July 2005 12:59 a.m.
To: [log in to unmask]
Subject: Re: Level of Evidence Assistance
Dear Colleagues,
Would any of you care to respond to Maria.
All good wishes,
Olive
>>> "Maria Shepherd" <[log in to unmask]> 06/29/05 7:21 pm >>>
Greetings-
I am doing a project for my physical therapy schooling, and I wanted to ask
for your input/assistance. I have two articles, both of which are
systematic reviews. However, they each only examine one RCT, and the
remaining articles reviewed (6 in one article and 10 in the other) are
empirical/observational studies which don't have control groups. All of the
findings were positive and concluded the same thing. I'm having trouble
assigning a level of evidence to these two systematic reviews because they
do only have one RCT. Would you mind providing me with some input as to
what level of evidence you might think they would be and why? I appreciate
your assistance.
Thank you.
Maria Shepherd, PT
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