Table 2.

Variable summary (mean ± SD) of monozygotic and dizygotic twin pairs^a.

Measure	Total (N = 182)	Monozygotic twins (MZ) (n = 110)	Dizygotic twins (DZ) (n = 72)	Mean (95% CI) Differenceb	pc
Arousal Index (events/hour)	12.56 ± 5.72	12.84 ± 5.81	12.14 ± 5.49	0.70 (−1.45 to 2.86)	.519
Average arousal duration (seconds)	7.51 ± 0.78	7.46 ± 0.79	7.58 ± 0.76	−0.12 (−0.39 to 0.16)	.395
Average arousal intensity scale	4.83 ± 0.85	4.77 ± 0.83	4.92 ± 0.89	−0.15 (−0.47 to 0.16)	.333
Slope of ΔHR per arousal intensity	2.55 ± 0.76	2.45 ± 0.69	2.70 ± 0.84	−0.25 (−0.53 to 0.02)	.074
Arousal intensity threshold of ΔHR	0.95 ± 0.89	0.97 ± 0.89	0.91 ± 0.91	0.06 (−0.25 to 0.37)	.702
Average ΔHR (min−1)	9.43 ± 3.80	8.90 ± 3.45	10.25 ± 4.17	−1.35 (−2.78 to 0.09)	.066
ΔHR at arousal intensity scale 4 (min-1)	7.49 ± 2.39	7.18 ± 2.31	7.96 ± 2.44	−0.78 (−1.68 to 0.12)	.090
ΔHR at arousal intensity scale 5 (min-1)	10.04 ± 2.87	9.63 ± 2.72	10.66 ± 3.01	−1.03 (−2.12 to 0.06)	.063
ΔHR at arousal intensity scale 8 (min-1)	17.68 ± 4.78	16.97 ± 4.38	18.76 ± 5.16	−1.79 (−3.59 to 0.01)	.051

Abbreviations: MZ, monozygotic; DZ, dizygotic; ΔHR, heart rate response to arousal; CI, confidence interval.

^aResults presented as mean ± SD.

^bDifference calculated as MZ value minus DZ value, estimated from mixed linear model.

^cp value from mixed linear model comparing MZ and DZ groups, controlling for possible correlation within MZ and DZ pairs.