Statistical tests
To compare the participants and their distribution in the two different groups, we used a Student t test, a chi-square test or a Fischer test. We used a Pearson correlation test to determine the correlation between age and the number of drugs. Statistical tests were performed with GraphPad Prism 5.0 (GraphPad Software, San Diego, CA). Values of probability lower than 5% (p < 0.05) were considered significant.