Anderson IM, Jones S, Twiss J. Do negative cognitive style and personality predict depression symptoms and functional outcomes in severe bipolar and unipolar disorders? Int J Cogn Ther. 2009 Dec 15;2(4):343-53. doi: 10.1521/ijct.2009.2.4.343
Hartman M, Bolton E, Fehnel SE. Accounting for age differences on the Wisconsin Card Sorting Test: decreased working memory, not inflexibility. Psychol Aging. 2001 Sep 1;16(3):385-99.