Fig. 2

Mean Plank Hold Time Standardized for BMI (sec/kg/m2) by Income. N = 676 (Boys n = 331, Girls n = 345). The number within each bar indicates the least squares mean value of the group. Each error bar indicates 95% confidence interval for the mean and was estimated after controlling for child’s age. a = significant difference between low (FIPR < 130%) and high (FIPR > = 350%) income groups, controlling for child’s age (p = 0.002). b = significant difference between middle (FIPR 130–349%) and high-income groups, controlling for child’s age (p = 0.029)