TABLE 1

Demographic Characteristics for Study Samples

VariableAged <8 Years (n = 14 972)Aged ≥8 Years (n = 21 833)
Age at first observation, mean (SD), y4.26 (2.27)11.49 (2.43)
Male7686 (51.34)11 375 (52.10)
Race
 White9650 (64.45)12 304 (56.36)
 African American4205 (28.09)8415 (38.54)
 Other1117 (7.46)1114 (5.10)
Fee group
 Low fee7365 (49.19)15 895 (72.80)
 Fee7461 (49.83)5801 (26.57)
 No fee99 (0.66)99 (0.45)
 High fee47 (0.31)38 (0.17)
Rural/urban code
 Urban10 090 (67.39)13 912 (63.72)
 Large rural area1748 (11.68)2910 (13.33)
 Small rural area1807 (12.07)2697 (12.35)
 Isolated1202 (8.03)2188 (10.02)
 Location unknown125 (0.83)126 (0.58)
Chronic disease3989 (26.64)5195 (23.79)
Periods of enrollment
 25597 (37.38)8465 (38.77)
 33230 (21.57)4659 (21.34)
 ≥46145 (41.04)8709 (39.89)
  • The descriptive statistics show the mean (SD) for age; for categorical variables such as gender and race, the number of respondents in the category are given as well as percentage of the full sample.