. Author manuscript; available in PMC: 2015 Aug 3.

Published in final edited form as: J Abnorm Psychol. 2013 Jul 8;122(3):842–853. doi: 10.1037/a0033079

Table 1.

Basic demographics and distribution of birth weight in each sample

	Georgia Sample	Tennessee Sample
Basic Demographics
Mean age (SD) in years	8.6 (2.6)	11.7 (3.3)
% Male	49%	49%
Ethnicity	87 % Caucasian, 8% African American	71% Caucasian, 24% African American
Mean mother’s age at twins’ birth (SD) in years	29.21 (4.47)	28.01 (5.34)
Zygosity	54% DZ, 46% MZ	63% DZ, 37% MZ
Mean gestational age (SD) in weeks	37.55 (3.35)	34.62 (3.32)
Distribution of Birth Weight
Mean birth weight (SD) in grams	2546.87 (585.79)	2434.66 (602.17)
25^th percentile (grams)	2211	2070
50^th percentile (grams)	2579	2466
75^th percentile (grams)	2948	2835
% ELBW (<1000 grams)	1.3%	2.1%
% VLBW (<1500 grams)	4.7%	7.8%
% LBW (<2500 grams)	45.7%	52.6%

Notes: ELBW indicates extremely low birth weight; VLBW indicates very low birth weight; LBW indicates low birth weight; MZ indicates monozygotic; DZ indicates dizygotic.