Table 1.

Participant demographics by group – including frequencies and percentiles of object permanence scores

	Very low birth weight N = 39	Full term N = 51
Demographic variables	Mean (standard deviation)
Child age, (months)	19.95 (1.35)	19.08 (1.31)
Birth weight (g)	949.71 (221.64)	3342.90 (420.66)
Gestational age (weeks)	27.38 (1.98)	39.23 (1.36)
Illness severity, no. of	24.87 (26.43)	0(0)
days on ventilation	24.87 (26.43)	0(0)
Family income*	3.21 (1.78)	2.82 (1.69)
Maternal education**	2.93 (1.56)	2.62 (1.78)
Maternal communication score	18.22 (3.15)	18.79 (4.16)
Bayley mental developmental  index	82.95 (15.32)	91.29 (11.61)
Object permanence scores
0 correct	8 (21%)	8 (16%)
1 correct	7 (18%)	0
2 correct	3 (7%)	0
3 correct	21 (54%)	43 (84%)

^*Based on semi-contnuous scores of 1: <$10000; 2: $10000–$20000; 3: $20000–$30000; 4: $30000–$40000; 5: $40000–$50000; 6: >$60000.

^**Based on semi-continuous scores of 1: <12th grade; 2: H.S; graduate; 3: 1 year college; 4: Associate degree; 5: Bachelor degree; 6: Some graduate school; 7: Masters degree or higher.