Evidence of the effect of clinical interventions in allergology, and in medicine as a whole, can be hierarchically
grouped based on the research design producing the evidence. The most weight is given to systematic reviews and metaanalyses,
and to randomised controlled trials. These trial designs are superior to non-randomised controlled trials and cohort
studies, which in turn are superior to case-control studies. The least weight is given to case-studies and anecdotal evidence.
Herein, the principles of evidence-based medicine and clinical study designs are reviewed in the context of examples
from the allergology literature.