50% adherence of patients suffering chronic conditions – where is the evidence?

The World Health Organization states that in a widespread report that “in developed countries, adherence among patients suffering chronic diseases averages only 50%”. We followed the quoted references to this statement. The data basis for this statement is one randomized controlled trial (RCT) on hypertensive steel workers in Canada published in 1975 and one study dealing with neurotic outpatients in Pennsylvania, USA published in 1965. Both studies are not suitable to assume such generalized adherence estimation and are not for different reasons transferable to today’s patient care.