Incidence of LLE refers to the number of new cases identified in a specified time period. Prevalence refers to the estimated population of children who are exhibiting LLE at any given time.
Estimates vary according to the definition and criteria used to identify LLE, as well as the age and characteristics of the population.
- Prevalence estimates of LLE in 2-year-old children primarily range between 10% and 20% (Rescorla, 1989; Rescorla & Alley, 2001; Roulstone, Loader, Northstone, Beveridge, & the ALSPAC Team, 2002; Zubrick, Taylor, Rice, & Slegers, 2007).
- In 18- to 23-month-old toddlers, the percentage of late talkers is estimated to be 13.5%. This rate rises to 16%-17.5% in 30- to 36-month-old children (Horowitz et al., 2003; Rescorla & Achenbach, 2002).
- Prevalence estimates based on both receptive and expressive language tend to be lower than those based on expressive language alone (13.4% versus 19.1%; Zubrick et al., 2007).
- Prevalence estimates are higher for children with a positive family history for LLE (23%) compared with those with no reported history (12%; Zubrick et al., 2007).
- Males are 3 times more likely than females to exhibit LLE (Zubrick et al., 2007).
- Higher prevalence rates of LLE have been noted in a population of toddler-age twins (38%) with a greater proportion in monozygotic twins (48.1%) compared with dizygotic twins (32.6%; Rice, Zubrick, Taylor, Gayan, & Bontempo, 2014).