Interestingly, for a millennium old problem, as of 2001, the most recent data, there have been only 19 adherence intervention studies that were randomized, had a control group, assessed adherence as opposed to only assessing clinical outcomes, also assessed outcomes, and provided a six month follow-up beyond the end of treatment to look at the stability of intervention assessment over time. There were only 19 studies that have been reported in the literature that set those criteria.