The probabilities of drop-out in the case of paroxetine and imipramine were 0.425 and 0.54 in the acute phase (6-week course), and 0.10 and 0.10 in the maintenance phase, respectively. The two drug therapies were shown to be equally effective in patients remaining in the clinical trial. However, given the significantly lower dropout rate of paroxetine, it was considered to be more effective than imipramine based on the intention to treat principle.