Onset of depressive episodes is faster in patients with bipolar versus unipolar depressive disorder: evidence from a retrospective comparative study.
Hegerl U, Bottner AC, Holtschmidt-Täschner B, Born C, Seemüller F, Scheunemann W, Schütze M, Grunze H, Henkel V, Mergl R, et al. J Clin Psychiatry. 2008 Jul; 69(7):1075-80.