The comparative clinical phenotype and long-term longitudinal episode course of bipolar I and II: a clinical spectrum or distinct disorders? - Judd,L.L.; Akiskal,H.S.; Schettler,P.J.; Coryell,W.; Maser,J.; Rice,J.A.; Solomon,D.A.; Keller,M.B. (Journal of Affective Disorders, 2003)