Effects of Birth Order on Temperament and Language
Birth order effects have been the subject of considerable research in the developmental literature. One aim of the present investigation was to explore links between temperament and birth order. Temperament should be linked to birth order. Because infant temperament is related to maternal stress during pregnancy (Huizink et al, 2002), and because mothers caring for children while pregnant presumably experience more stress, laterborn children could have different temperamental profiles than earlier-born children. Research has also shown reliable links between birth order and vocabulary size in infancy; with second born children demonstrating significantly larger vocabularies at 21 months (Oshima-Takane et al., 1996). However, to our knowledge, no studies have investigated the relationship between birth order and gestural productivity. Because gestural production is linked to language development (Iverson & Goldin-Meadow, 2005), it stands to reason that birth order should also be linked to gestural production. Thus, our second aim was to evaluate the relationship between birth order and gestural production. Eighty-three children (32 girls) visited the lab at M = 15.45 months (SD = 1.92 months). Caregivers completed the Infant Behavioral Questionnaire-Revised (IBQ-R), the MacArthur-Bates Communicative Development Inventory: Words and Gestures (MCDIWG), and a demographic questionnaire assessing family size and birth order. The IBQ-R produced three overarching superdimensions: surgency, negative affectivity, and effortful control. Gestural productivity was derived from the MCDI-WG. In line with our first aim, we evaluated correlations between infant temperament and birth order. These analyses revealed a significant and positive relationship between later-born status and temperamental negative affectivity (r = .27, p = .03), indicating that later-born children were rated by mothers as temperamentally more negative in affective expression. Neither other temperament superdimension was related to birth order. Follow-up analyses revealed that sadness was the only subdimension of negative affectivity to be associated with later-born status (r = .31, p < .01). To investigate whether birth order was related to gestural production, we analyzed correlations between birth order and the MCDI-WG categories of "performing actions with objects" and "imitation". Positive and significant associations between birth order and both gestural production measures were found (performing actions with objects, r = .30, p = .03; and imitation, r = .35, p < .01). Although these results were in line with our expectations, they remain to be supported by replication. In the meantime, these results suggest interesting findings for both temperament and language researchers. First, later born children appear more at risk for temperamental difficulty. The source of this risk could include heightened maternal prenatal stress during pregnancy. But the source could also be postnatal, perhaps exacerbated by later-borns spending proportionally less time with caregivers, or more time sharing with siblings. Secondly, the gestural production results suggest that later born children are at a particular advantage. This advantage may be due to the fact that later born children, by virtue of their larger families, have more mode.
Rookstool, Kelsey; Long, Kelsey; Driggers-Jones, Lauren P.; and Dixon, Wallace E.. 2018. Effects of Birth Order on Temperament and Language. Poster Presentation. Biennial Meetings of the International Congress of Infant Studies, Philadelphia, PA. https://infantstudies.org/wp-content/uploads/2018/06/ICIS-ABSTRACT-BOOK-DAY-2-MONDAY-2-JULY.pdf