Family constellation and cognitive development in three-and five-year-old children from the Millennium Cohort Study

Abstract

Using data from the British Millennium Cohort Study, this dissertation studies the effect of the family constellation on the cognitive development levels of children at the ages of three and five years. The first paper looks at the correlation between family size, birth order and the age gap between sibling births and cognitive ability test results at the ages of three and five years. For three-year-olds, family size and birth order are negatively correlated with vocabulary scores and school readiness scores. Larger age gaps between subsequent children have the potential to mitigate this impact. At the age of five years, family size is still negatively correlated with vocabulary and spatial reasoning test scores. While birth order is negatively correlated with vocabulary scores, it is positively correlated with spatial reasoning scores. Spacing between siblings still has an ameliorating effect for the younger sibling, yet is somewhat weaker than at the age of three. Interestingly, family constellation aspects have no statistical relationship to non-verbal reasoning (picture similarity) scores at age five. Paper two investigates the relationship between the family constellation and the progress of children's vocabulary ability between the ages of three and five years. The results give limited evidence that family size has a statistical, or sizeable, relationship with the progress of children's cognitive ability. Rather, children of higher birth order and those raised by single parents show, on average, smaller rates of progress between the ages of three and five. Single parenting has the greatest (negative) effect on those children with higher levels of initial ability. The third paper uses an instrumental variable approach to account for problems resulting from endogenously determined family size. Twins at last birth is used to instrument for family size. Results indicate that while there is a negative relationship between family size and children's cognitive outcomes, the relationship is weak. Rather, there is stronger evidence for birth order driving the differences in cognitive scores. Evidence pertaining to the effect of the spacing between a child and its older sibling suggests that greater spacing may be beneficial for the younger sibling. Show more