A Study of the Effect of Birth Interval on the Development of 9-year-old Schoolchildren in Singapore

Abstract

The effect of birth interval on some physical and mental aspects of 9-year old children was studied in Singapore between September 1974 and July 1975. Birth interval falls into 2 main categories -- B1, the interval preceding the birth of the index child and B2, the interval following the birth of the child. It was hypothesized that the shorter the interval B1 the lower the vocabulary score and general attainment of the index child would be and the shorter the interval B2 the lesser the physical growth of the index child would be. A significant difference was found in the Mill Hill vocabulary score, Raven's Progressive Matrices score, as well as height and weight for children born with varying birth intervals. Children with shorter B1 intervals do score lower than those with longer B1 intervals, there being a gradual improvement as B1 progresses from less than 12 months to over 24 months. The relationship is linear. The effect of B2 is less marked and is inconsistent. The most striking correlation is between B1 and vocabulary score, B1 accounting for about 39% of the variation in the Mill Hill test. B2 does not have as great an effect as expected on height and weight, but it was significant at the 5% level for height. B1 is again more important. In both height and weight, neither birth interval is as important as in the verbal and perception tests. Neither family size nor language spoken at home affect the vocabulary score to any significant extent. Income does have an association with all 4 major variables considered and is 2nd in importance to B1 as a predictor variable in the cases of vocabulary score and Raven's score.