Most if not all participants with melancholic depression will have been experiencing insomnia at baseline. To show that the improved efficacy of high dose quetiapine (150-300 mg/day) for participants with melancholic depression was not simply due to the sleep-inducing properties of quetiapine, the researchers will conduct a Cox regression (Analysis E) comparing modified MADRS response rates between the quetiapine (150-300 mg/day) and placebo groups, while including the categorical melancholic depression grouping variable as a covariate and testing for an interaction between treatment group (quetiapine 150-300 mg/day vs placebo) and melancholic depression (present vs not present). Because the modified MADRS response rates do not include a "reduced sleep" item, if there is a significant interaction suggesting higher modified MADRS response rates in persons with melancholic depression, the researchers can reasonably conclude that the superiority of high-dose quetiapine for people with melancholic depression was not simply due to its ability to induce sleep in these participants.