2018 Sat Session B 1000

Saturday, November 3, 2018 | Session B, Conference Auditorium | 10am

You best have a sister: The effect of siblings on language development as a function of age-gap and sex
N. Havron, A. Cristia, F. Ramus, H. Peyre

The number of older siblings that a child has is negatively correlated with their verbal skills (e.g., Peyre et al, 2016). Since both the quality and the quantity of adult child-directed speech contribute to language development (e.g., Ramirez-Esparza, Garcia-Sierra, & Kuhl, 2014), siblings may negatively impact language because parents can allocate less undivided attention to each child. However, as children do tend to observe, imitate, and seek assistance from older siblings (Azmitia & Hesser, 1993) – siblings themselves might be able to, at least partially, compensate for this resource-competition by talking to the younger child. To test the role of both these factors, competition and compensation, we analyze data collected as part of the EDEN cohort (Heude et al, 2016), which contains background information and language scores at two, three, and five years of age for over 1,000 French children. We focused on two variables that may allow us to tease apart positive and negative effects of having siblings: Age-gap, sex, and their interaction.

Age-gap: When the age-gap between the target child and the sibling is small, then the sibling is relatively young, and will thus require more parental resources than an older sibling (i.e., one with a greater age-gap). In addition, siblings with a greater gap (i.e., older) will have relatively better language and theory-of-mind skills, and thus may provide better quality input than those with a smaller gap. For both these reasons, we predicted that the age-gap between siblings would be positively correlated with language outcomes in the target children.

Sex: Sisters are more likely to engage in nurturing behavior than brothers (e.g., Tucker, McHale, & Crouter, 2001). We therefore predicted higher language scores for children who have a sister than a brother.

Age gap by Sex interaction: Small gap sisters are likely as demanding as small gap brothers, and just as bad at providing quality input. At large age gaps, however, older sisters would be more likely to care for their sibling. Therefore, we predicted a greater effect of age-gap for sisters than for brothers.

Focusing on children who had only one older sibling (n=451), we predicted z-scored language outcomes from age-gap, sex of the older sibling, and an interaction (control variables listed in table 1, analysis preregistered on OSF). We found that children with an older sister indeed had higher language scores than those with brothers. In fact, the negative effect of having a sibling versus no sibling was only true for those who had a brother: Children who had an older sister had similar language scores to children with no siblings. The effect of sex fits with the idea that input from siblings can make up for loss parental input. However, contrary to our prediction, age-gap had a negative effect on language scores, with no interaction (see table 1 and fig.2). Our ongoing work aims to investigate possible explanations for this surprising result. For now, we can conclude that it is  better to have an older sister than an older brother.