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Illustration of the association between phase delays of the melatonin midpoint and sleep parameters in individual older subjects. Habitual sleep onset and sleep offset is depicted by the beginning and end of the gray bar. Phase delays are the difference between baseline (■) and post-treatment (□) melatonin midpoints. Both early wake times and/or a smaller interval between sleep offset and baseline circadian phase (e.g. melatonin midpoint) were associated with smaller phase shifts.
