As Dr Evans points out, patients scheduled for major surgery may well have elevated anxiety levels. This may have resulted in elevated presurgical depression ratings. The psychiatric diagnoses, on the other hand, were lifetime diagnoses (as per Feighner et al1), and thus the excess found presurgically cannot wholly be attributed to the situation of awaiting surgery. For example, hysteria (Briquet's disorder) was diagnosed on the basis of "chronic recurrent illness beginning before age 30." Inclusion of a control or comparison group (eg, patients scheduled for other major surgery) would have been useful, however, and should be included in any future investigations.
Martin RL. Psychiatric Status After Hysterectomy-Reply. JAMA. 1981;245(18):1818. doi:10.1001/jama.1981.03310430011005