Changes in Word Usage Frequency May Hamper Intergenerational Comparisons of Vocabulary Skills

Abstract

Research on secular trends in mean intelligence test scores shows smaller gains in vocabulary skills than in nonverbal reasoning. One possible explanation is that vocabulary test items become outdated faster compared to nonverbal tasks. The history of the usage frequency of the words on five popular vocabulary tests, the GSS Wordsum, Wechsler Adult Intelligence Scale (WAIS), Wechsler Adult Intelligence Scale–Revised (WAIS-R), Wechsler Intelligence Scale for Children (WISC), and Wechsler Intelligence Scale for Children–Revised (WISC-R) IQ tests, was analyzed by means of the Google ngram viewer. Usage frequency had a 0.38 to 0.73 correlation with item difficulty. In the period between test standardizations, the median change in usage frequency was −17% for WISC words, −8% for Wordsum, −5% for WISC-R, −4% for WAIS, and 0% for WAIS-R words. The correlation between median change in usage frequency and gain in vocabulary score was 0.33. Further studies with a larger set of vocabulary tests are needed to analyze in more detail the magnitude of the effect of changing word usage frequencies.