Effectiveness studies: advantages and disadvantages.

In recent years, so-called "effectiveness studies," also called "real-world studies" or "pragmatic trials," have gained increasing importance in the context of evidence-based medicine. These studies follow less restrictive methodological standards than phase III studies in terms of patient selection, comedication, and other design issues, and their results should therefore be better generalizable than those of phase III trials. Effectiveness studies, like other types of phase IV studies, can therefore contribute to knowledge about medications and supply relevant information in addition to that gained from phase III trials. However, the less restrictive design and inherent methodological problems of phase IV studies have to be carefully considered. For example, the greater variance caused by the different kinds of confounders as well as problematic design issues, such as insensitive primary outcome criteria, unblinded treatment conditions, inclusion of chronic refractory patients, etc, can lead to wrong conclusions. Due to these methodological problems, effectiveness studies are on a principally lower level of evidence, adding only a complementary view to the results of phase III trials without falsifying their results.