Estimated sleep duration (h/d). (A) gender and age: Boys 9–10 y, n = 181; Boys 11–12 y, n = 66; Girls 9–10 y, n = 183; Girls 11–12 y, n = 53. (B) race/ethnicity: Black, n = 150; Hispanic, n = 333. (C) obesity status: Normal, n = 164; Overweight, n = 84; Obese, n = 235. (D) socioeconomic status (SES): High SES, n = 33; Low SES, n = 450. (E) weekend/weekday: Weekdays, n = 483; Weekend days, n = 479. The whisker represents the standard error of the mean. Different letters (a, b) above the columns in each figure indicate a significant difference.