Table 2.

Enjoyment: twin correlations and ACE parameters.

Enjoyment	Country	School subject	MZ	DZss	A/D	C	E
9 years	UK	Math	.38 (N = 1192)	.14 (N = 1049)	.38	.00	.62
		English	.41 (N = 1197)	.22 (N = 1051)	.38	.03	.59
		Science	.33 (N = 1185)	.18 (N = 1047)	.30	.03	.67
	Germany	Math	.38 (N = 133)	.20 (N = 121)	.36	.02	.62
		German	.31 (N = 133)	.29 (N = 121)	.04	.27	.69
10 years	Canada (Québec)	Math	.34 (N = 153)	−.14a (N = 108)	.34	.00	.66
		Reading	.46 (N = 153)	.02a (N = 108)	.46	.00	.54
	Japan	Math	.50 (N = 109)	.21a (N = 77)	.50	.00	.50
11 years	Germany	Math	.48 (N = 133)	.24 (N = 121)	.48	.00	.52
		German	.60 (N = 133)	.30 (N = 121)	.60	.00	.40
	Japan	Math	.50 (N = 107)	.28 (N = 68)	.44	.06	.50
12 years	UK	Math	.46 (N = 2020)	.20 (N = 1823)	.46	.00	.54
		English	.48 (N = 2020)	.20 (N = 1817)	.48	.00	.52
		Science	.43 (N = 2016)	.22 (N = 1816)	.42	.01	.57
	Canada (Québec)	Math	.42 (N = 147)	−.01a (N = 111)	.42	.00	.58
		Reading	.59 (N = 147)	.27 (N = 111)	.59	.00	.41
	Japan	Math	.48 (N = 125)	−.03a (N = 62)	.48	.00	.52
	USA	Reading	.63 (N = 146)	.15 (N = 202)	.63	.00	.37
13 years	Germany	Math	.42 (N = 133)	.16a (N = 121)	.42	.00	.58
		German	.49 (N = 133)	.04a (N = 121)	.49	.00	.51
	Japan	Math	.53 (N = 91)	−.03a (N = 31)	.53	.00	.47
16 years	UK	Math	.42 (N = 817)	.21 (N = 710)	.42	.00	.58
	Japan	Math	.58 (N = 68)	.31a (N = 32)	.58	.00	.42
	Russia	Math	.41 (N = 34)	.15a (N = 34)	.41	.00	.59

Note. MZ intra-class correlations (ICCs), same-sex DZ (DZss) ICCs, and genetic (A), shared environmental (C) and non-shared environmental (E) estimates. The results were controlled for age and sex. ACE estimates were derived from ICCs using Falconer’s formula. A/D = where DZ ICC is less than half of that of MZ ICC, non-additive genetic (D) effects are implied; in these cases A and D effects cannot be disentangled.

^aDZ ICC did not reach significance.