Figure 4.

Onset ages for Bellevue (green) and Langone (purple) samples. (A) Walk onset age. (B) Crawl onset age. Each symbol represents data from one infant. Horizontal black bars denote group averages. Asterisks denote significant group differences (*p < .05). Based on standards published by the World Health Organization (WHO), blue bands denote the 25^th to 75^th percentiles for walk and crawl onset ages; dashed blue lines denote the 10^th and 90^th percentiles. Across samples, walk onset age ranged from 8 to 18 months and crawl onset age ranged from 6 to 12 months. The distributions for onset ages in Langone infants straddles the 25^th-75^th percentiles, with approximately equal numbers of infants outside the 10^th and 90^th percentiles for walking and disproportionately more infants with early onset ages for crawling. In contrast, the distributions for onset ages in Bellevue infants are primarily beyond the 75^th percentile, with disproportionately more infants beyond the 90^th percentile for both walking and crawling.