The Association between Parental Socioeconomic Status and Intellectual Ability in Japanese Infants aged 42 month: The Hokkaido Study

INTRODUCTION: According to a 2012 UNICEF report the relative poverty rate of Japanese children is 14.9%. While many Western studies have shown that academic ability of children from low-income families is relatively low, few studies from Japan that have investigated children’s ability and parental income. Thus, the aim of this study was to investigate differences in intellectual ability in infants aged 42 months according to prenatal family income in a prospective birth cohort. 

METHODS: A total of 514 pregnant women attending an obstetrics clinic in Sapporo between 2002 and 2004 were enrolled in the study. After obtaining informed consent, participants filled out a questionnaire about their socio-economic status and lifestyle. Next information was obtained on the type of birth, maternal depression, the child’s home environment and intellectual ability at 42 months. Data from 144 mother-child pairs were used in the final analysis. Data on household income was divided into 3 groups: <3 million yen, 3-5 million and >=5 million. K-ABC was used to assess intellectual ability and achievement scales (AS), mental processing scales (MP), sequential processing scales (SEQ), and simultaneous processing scales (SIM) were calculated. A general linear model (GLM) was used in the analysis.

RESULTS: Average K-ABC scores (±SD) were AS 98.4(±15.8), MP 101.4(±15.3), SEQ 97.8 (±18.8), and SIM 103.1 (±15.7). In the GLM, the point estimate of infants with mothers ranked in the highest income increased as follows: AS 6.08 (95% CI; 2.52-9.71), MP 8.00 (4.47-11.52), SEQ 8.33 (3.35-12.81), and SIM 6.85 (3.21-10.49).

CONCLUSIONS: We found a significant difference in the intellectual ability of Japanese infants aged 42 months according to prenatal family income. In order to reduce the gap in children’s development relative to parental income, further studies are necessary.