Fitting interventions into these
categories is not always straightforward. For one thing, the categories
represent a mix of several hierarchies: the level of benefit (or harm), the
level of evidence (RCT or observational data), and the level of certainty around
the finding (represented by the confidence interval). Another problem is that
much of the evidence that is most relevant to clinical decisions relates to
comparisons between different interventions rather than to comparison with
placebo or no intervention. Where necessary, we have indicated the comparisons.
A third problem is that interventions may have been tested, or found to be
effective, in only one group of people, such as those at high risk of an
outcome. Again, we have indicated this where possible. But perhaps most
difficult of all has been trying to maintain consistency across different
topics. We are working on refining the criteria for putting interventions under
each category.