Paul Glasziou wrote:
> In most levels of evidence (e.g., see
> http://www.cebm.net/levels_of_evidence.asp )
> a systematic review (of randomised trials) is the top level: Level 1
I think that the "hierarchy" may change according to the type of
question asked (therapy, diagnosis etc)
For questions about therapy, I would also consider that the EBM Working
Group (user'Guide), quite reasonnably put the N-of-one study on top.
Of course, the N-of-1 study only apply to the care of a sigle patient.
Still, the opportunity of doing it should be considered in systematic
review and guidelines.
There is also some evidence that a systematic review of small RCTs is no
better than a single large RCT.
As you pointed out, weheter a systematic review includes or not a
meta-analysis (ore more) will depend from the nature of the available
data and would not change much by itself the strength of the evidence.
so my preferred hierarchy for a question about therapy would be:
N-of-1 study (rarely doable or done)
Systematic review wich includes large RCTs
Single large RCT
Systematic review of non-large RCTs
Single non-large RCT
etc
How much this view is shared?
cheers,
Piersante Sestini
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