Study groups drawn from treatment-seeking populations are biased toward relative illness severity and persistence. By the same token, patients who are attending a clinic more frequently are more likely to be in a problematic phase of their illness than those with less frequent visits. If the group described by Tondo et al. was drawn from all of those "attending" a clinic in a given period of time, those who were experiencing a relatively difficult period in their illness would be overrepresented, and this would produce the impression that current therapies are less effective than past therapies. The prospective ascertainment of illness course provided with our data avoids this problem in that patients were tracked regardless of whether, or how often, they continued to seek treatment.