TABLE 1.

Group means (standard deviations) of combat-exposed Vietnam veterans with and without PTSD and their combat-unexposed, identical co-twins

	---------PTSD pairs*--------				-------Non-PTSD pairs†------				--------------------Mixed Model--------------------						---Independent t-tests---
	Exposed		Unexposed (high-risk)		Exposed		Unexposed (low-risk)		Diagnosis		Exposure		Interaction		Exposed		Unexposed
	(n =18)		(n = 18)		(n = 23)		(n = 23)		t(39)	p	t(40)	p	t(39)	p	t(39)	p	t(39)	p
Age (years)‡	52.8	(3.4)	52.8	(3.4)	51.8	(2.3)	51.8	(2.3)	-	-	-	-	-	-	1.1	0.27	1.1	0.27
CAPS§	73.3	(16.9)	-	-	6.2	(7.3)	-	-	-	-	-	-	-	-	17.2	<0.001	-	-
Combat severity¶	7.7	(2.1)	-	-	3.5	(2.6)	-	-	-	-	-	-	-	-	5.6	<0.001	-	-
Traumatic events╢	8.1	(2.6)	5.2	(3.7)	5.1	(4.0)	4.2	(3.0)	2.6	0.01	2.4	0.02	1.3	0.20	2.8	0.009	1.0	0.34
MAST**	19.1	(17.6)	6.4	(10.2)	2.4	(4.5)	2.5	(4.0)	4.5	<0.001	2.8	0.007	2.8	0.007	4.4	<0.001	1.7	0.10
Depression††	2.5	(0.9)	0.3	(0.5)	0.6	(0.7)	0.4	(0.5)	4.6	<.001	5.3	<0.001	6.9	<0.001	7.4	<0.001	0.7	0.51

^*As determined by the presence of current, combat-related PTSD in the combat-exposed twin

^†As determined by the absence of current or past, combat-related PTSD in the combat-exposed twin

^‡As of October 1, 2000

^§Clinician-Administered PTSD Scale (range 0–136)

^¶18-item measure (range 0–18)

^╢Number of potentially traumatic lifetime non-combat events

^**Michigan Alcoholism Screening Test (range 0–25)

^††Symptom Check List-90-Revised Depression Subscale (range 0–4)