Table 1.

Summary statistics for MZ and DZ twins. N male and N female represent the number of complete male and female twin pairs with non-missing data for all three measures of civic engagement.

	MZ				DZ
	mean	s.d.	N male	N female	mean	s.d.	N male	N female
civic engagement	0.04	1.29	352	387	−0.06	1.31	183	226
volunteering	2.09	0.85	352	387	2.04	0.84	183	226
donating	2.31	0.89	352	387	2.24	0.90	183	226
voting	3.24	0.93	352	387	3.23	0.99	183	226
verbal IQ	96.38	13.88	312	365	96.38	13.31	162	207
performance IQ	106.94	17.27	289	342	106.88	17.03	158	182
full IQ	100.97	14.56	289	342	100.90	13.77	158	182
positive emotionality	122.83	12.96	342	368	123.00	13.32	176	221
negative emotionality	78.97	13.30	342	368	79.49	13.81	176	221
constraint	143.96	15.13	342	368	143.01	16.21	176	221
age	29.45	0.67	352	387	29.35	0.67	183	226
male	0.48	0.50	352	387	0.45	0.50	183	226