A total of 209 university undergraduates entered 18 encounter groups which met for a total of 30 hours. Thirty-nine subjects dropped out of the groups, while 170 completed the group experience. Of these, 16 subjects were considered "casualties"—defined as an enduring, significant, negative outcome which was caused by their participation in the group. The most reliable method of identifying casualties was to solicit the opinions of the other group members; the leader was not a valuable judge of casualty states. The frequency, severity, and mode of psychological injury varied considerably amongst the 18 groups. The highest-risk leadership style was characterized by high stimulus input, aggressivity, charisma, support, intrusiveness, individual (as opposed to interpersonal or group) focus. The most vulnerable individuals were those with low self-concept and unrealistically high expectations and anticipations of change.
Yalom ID, Lieberman MA. A Study of Encounter Group Casualties. Arch Gen Psychiatry. 1971;25(1):16-30. doi:10.1001/archpsyc.1971.01750130018002