Later research showed that cases of depression caused by external factors, such as pressure and personality, were in fact only a small number of the total; 85 % of cases were in fact related to physical problems--the underlying causes of depression.
隨後的研究才確定，外因性的憂鬱症，即所謂發病與外界環境因素有關，如壓力和性格就屬此類，只佔少數；百分之八十五的憂鬱症是體質問題，即所謂的「內因性憂鬱症」。