Table 1.

4 × 4 correlation matrix for 5 zygosity by sex groups

	Mother twin 1	Father twin 1	Mother twin 2	Father twin 2
Mother twin 1	1	Parental agreement correlation	Mother correlation twin1–twin2	Mother (twin1)–father (twin2) cross-correlation
Father twin 1	Parental agreement correlation	1	Father (twin1)–mother (twin2) cross-correlation	Father correlation twin1–twin2
Mother twin 2	Mother correlation twin1–twin2	Father (twin1)–mother (twin2) cross-correlation	1	Parental agreement correlation
Father twin 2	Mother (twin1)–father (twin2) cross-correlation	Father correlation twin1–twin2	Parental agreement correlation	1