. Author manuscript; available in PMC: 2008 Jun 26.

Published in final edited form as: Psychiatr Clin North Am. 2008 Jun;31(2):157–177. doi: 10.1016/j.psc.2008.02.001

Table 3.

Twins Studies in Which one Twin has Committed Suicide^*

	No. of twins (%) concordant for suicide behavior
Study	MZ	DZ	P
Haberlandt [1967]	14/51 (17.6)^a	0/98 (0)	< 0.001
Juel-Nielsen [1970]	4/19 (21.1)	0/58 (0)	< 0.003
Zair [1981]	1/1 (100)	0/0 (0)	NS
Roy et al. [1991]	7/62 (11.3)	2/114 (0)	< 0.01
Roy et al. [1995]	10/26 (38.5)^b	0/9 (1.7)	< 0.04
Roy and Segal [2001]	4/13 (30.7)^c	0/15 (0)	< 0.04
Total	40/172 (23.0)	2/294 (0.7)	< 0.00001

Five pairs, co-twin attempted suicide.

Ten pairs, co-twin attempted suicide.

Three pairs, co-twin attempted suicide.

From Brent and Mann. Family genetic studies, suicide, and suicidal behavior. Am J Psychiatry 2005;133C:13–24, with permission.