Number of words at age 2.5 years is associated with intellectual functioning at age 7 years in the SELMA study

We examined the association between the number of words used at age 2.5 years and deficits in intellectual functioning at age 7 years, in 549 children, and whether such association is confirmed by parental concern about the child's development.

Parental reports of how many words their children used at age 2.5 years were analysed for the association to intellectual functioning (assessed with Wechsler Intelligence Scale for Children - Fourth Edition,WISC-IV) at age 7 years using linear regression, adjusting for sex, maternal education level, parental IQ and smoking during pregnancy. Parental concern at age 7 years was examined with the Early Symptomatic Syndromes Eliciting Neurodevelopmental Clinical Examinations-Questionnaire (ESSENCE-Q).

Adjusted linear regression showed that use of 50 words or fewer at age 2.5 years, relative to use of more than 50 words, was associated with lower scores of Full-scale IQ (B = 7.27, p = 0.001), verbal comprehension (B = 8.53, p < 0.001), working memory (B = 9.04, p < 0.001) and perceptual reasoning (B = 4.21, p = 0.045), in the WISC-IV, at age 7 years. Parental concern was more common in the group that used 50 words or fewer (Mann-Whitney U test, p = 0.011).

This easily accessible measure of number of words seems to be a valuable marker for intellectual functioning later in life.