Purpose of review: Meta-analysis provides the highest level of evidence-based efficacy of a medical treatment or intervention. Allergen immunotherapy in its two forms of subcutaneous immunotherapy and sublingual immunotherapy (SLIT) is an effective treatment of respiratory allergy as shown by meta-analyses, but in recent years there has been an overflow of meta-analyses on SLIT, with contrasting results that may generate confusion among physicians.
Recent findings: It can be observed that flaws are often present in meta-analyses including: incorrect selection of trials, inappropriate use of evaluation parameters for the analysis, and unsuitable analyses. For instance, it is clear that a meta-analysis of several small studies does not predict the results of a single large study that remains the gold standard to assess the efficacy and safety of a treatment. To assess the interest of the matter, we calculated the number of citations of meta-analyses on SLIT efficacy in the 10 years after the first publication in 2005 and detected a continuous decrease in citations.
Summary: Today, the appropriateness of a meta-analysis should be carefully evaluated, taking into account that a meta-analysis uses a statistical approach to combine the results from multiple small studies to increase power, to improve estimates of the size of the effect, and/or to resolve uncertainty when reports disagree. Editors and reviewers of medical journals should consider that to judge a meta-analysis requires a high level of expertise that is obvious in reviewers belonging to the Cochrane organization.