Dickerson et al. BMC Public Health 2011, 11:926 http://www.biomedcentral.com/1471-2458/11/926 Table 1 Descriptive Statistics by Body Mass Index (n = 1,981) *Age Sex Male Female Not Provided Race/Ethnicity Non-Hispanic White African-American Hispanic Not Provided *Educational Attainment (1 = First Grade, 17 = Graduate School) Rurality Urban Rural Hours per day spent watching television Less than 1 h 1-2 h 2-4 h 4-6 h More than 6 h Not Provided *Minutes per week of moderate physical activity Body Mass Index Classification (World Health Organization) Normal Overweight Obese Weight Class I (n = 477) (n = 664) (n = 427) 61.96 (±15.00) 61.70 (±13.34) 59.09 (±12.95) 107 (22.4%) 370 (77.6%) 0 (0.0%) 236 (35.5%) 428 (64.5%) 0 (0.0%) 151 (35.4%) 276 (64.6%) 0 (0.0%) Obese Class II (n = 177) 56.45 (±10.88) 58 (32.8%) 184 (67.2%) 0 (0.0%) Obese Class III (n = 236) 54.65 (±13.61) 38 (16.1%) 174 (73.7%) 24 (10.2%) Total (n = 1,981) 59.96 (±13.73) 590 (29.8%) 1,367 (69.0%) 24 (1.2%) 409 (85.8%) 558 (84.1%) 341 (79.9%) 136 (76.8%) 130 (55.1%) 1574 (79.4%) 32 (6.7%) 44 (6.6%) 46 (10.8%) 18 (10.2%) 44 (18.6%) 184 (9.3%) 23 (4.8%) 46 (6.9%) 33 (7.7%) 19 (10.7%) 37 (15.7%) 158 (8.0%) 13 (2.7%) 16 (2.4%) 7 (1.6%) 4 (2.3%) 25 (10.6%) 65(3.3%) 13.68 (±2.68) 13.81 (±2.46) 13.62 (±2.50) 13.32 (±2.40) 12.34 (±2.91) 13.53 (±2.60) 302 (63.3%) 410 (61.7%) 175 (36.67%) 254 (38.3%) 60 (12.6%) 142 (29.8%) 165 (34.6%) 57 (11.9%) 43 (9.0%) 10 (2.1%) 209.27 ± (328.32) 72 (10.8%) 198 (29.8%) 247 (37.2%) 87 (13.1%) 49 (7.4%) 11 (1.7%) 199.19 ± (366.12) 251 (58.8%) 176 (41.2%) 30 (7.0%) 109 (25.5%) 149 (34.9%) 81 (19.0%) 48 (11.2%) 10 (2.3%) 206.99 ± (422.37) 102 (57.6%) 75 (42.4%) 152 (64.4%) 84 (35.6%) 1217 (61.4%) 764 (38.6%) 15 (8.5%) 34 (19.2%) 73 (41.2%) 29 (16.4%) 24 (13.6%) 2 (1.1%) 165.06 ± (381.67) 19 (8.1%) 45 (19.1%) 62 (26.3%) 38 (16.1%) 38 (16.1%) 34 (14.4%) 109.05 ± (291.52) 196 (9.9%) 528 (26.7%) 696 (35.1%) 292 (14.7%) 202 (10.2%) 67 (3.4%) 190.87 ± (365.95) Page 6 of 10 X2 p 71.837 <0.001 43.79 <0.001 124.47 <0.001 43.6 3.97 <0.001 0.41 54.03 <0.001 77.65 <0.001 * Chi-squared statistics based on the Kruskal-Wallis equality of populations rank test Note–Statistical significance is determined using the Bonferroni correction. Based on 7 comparisons in the analysis, the level of statistical significance is a = 0.007 Simultaneous quantile regression–similarity of effect by BMI classification The F tests in Figures 1 and 2 evaluate the hypoth- esis that the effect of each independent variable on BMI is the same by BMI classification. Rejecting the hypothesis (i.e., when an F statistic yields a p-value less than the alpha level of statistical significance of 0.05) indicates a heterogeneity effect of the independent vari- able on BMI by BMI classification. For example, when evaluating the effect of watching television on BMI clas- sification (the graph in the upper left quadrant of Figure 1), the F statistic measuring the effect of watching televi- sion between normal weight BMI classification and overweight BMI classification is 5.57 which generates a p-value of 0.018. This allows us to reject the hypothesis (since the p-value is below the alpha level of significance of 0.05) that the effect of watching television on BMI is the same between normal weight BMI classi- fication and overweight BMI classification. Using these analyses, it becomes clear that variables relating to PA and sedentary behavior become more meaningful among participants in higher BMI classifications. Figure 1 illustrates the effect of watching television, moderate PA, self-reporting as African-American, and self-reporting as Hispanic on BMI classification. The effect of watching television on BMI was statistically sig- nificant for all BMI classifications except normal weight. The difference from normal weight and overweight demonstrated a positive heterogeneous effect. The effect of moderate PA on BMI was statistically significant for all BMI classifications except normal weight and over- weight. The difference between obese class I and obese class II demonstrated a negative heterogeneous effect. The effect of self-reporting as African-American on BMI was statistically significant for all BMI classifications except normal weight. The difference between normal weight and overweight demonstrated a positive hetero- geneous effect. The effect of self-reporting as Hispanic was only statistically significant for the classifications of normal weight, overweight, and obese class I. None of