Comparing SES Measures as Predictors of Bilingual Vocabulary Size in Norway and South Africa

In child language research, lower socioeconomic status (SES) is found to be related to poorer language outcomes. Bilingual children’s language proficiency is influenced by the exposure they receive in each language, and SES is often used as a proxy to determine the quality and quantity of this language exposure. Using SES as a proxy for input in bilingual families is challenging, as parental proficiency in the majority language might be low, while proficiency in the minority language might be high, affecting the quality and quantity of language input that a child receives (O’Toole et al., 2017). The current study sets out to determine which measure(s) of SES are best suited to predicting bilingual vocabulary size, and whether these are the same across two global contexts, namely Norway and South Africa. Arguably, the most commonly used proxy to measure SES in child language research is maternal education, and it has been found to predict the variability in L2 vocabulary scores (e.g., Hammer et al., 2012). However, Sorenson Duncan and Paradis (2020) investigated maternal education and its effect on language development in 4- to 5-year-old bilingual children and found that this relationship is more complex in bilingual families because the mother’s fluency in the L2, the quantity of L2 use and the language that the mother’s education was undertaken in, all influenced language outcomes. A study from Malta investigated which of four SES factors and a composite SES score was the best predictor of lexical outcomes in 3- to 4-year-old bilingual children (Gatt et al., 2020); the authors found that these measures of SES were not interchangeable and that the composite SES score was the best predictor of lexical knowledge, in line with findings from De Cat (2021).