Table 1.
Summary of Sample Characteristics in the National Institutes of Health Magnetic Resonance Imaging Study of Normal Brain Developmenta
| Variable | Mean (Range) |
|---|---|
| Male | 0.475 (0–1) |
| Nonwhite | 0.147 (0–1) |
| Hispanic | 0.122 (0–1) |
| Birth weight, oz | 126 (86–182) |
| Age, y | 12 (4–22) |
| Scans, No. | 2.12 (1–3) |
| Age at first scan, y | 11.1 (4–20) |
| Family size | 5.39 (2–14) |
| Education level | |
| Less than high school | 0.008 (0–1) |
| High school | 0.144 (0–1) |
| Some college | 0.302 (0–1) |
| College | 0.323 (0–1) |
| Some graduate school | 0.056 (0–1) |
| Graduate school | 0.168 (0–1) |
| Income | |
| Relative to the FPL, % | 360.7 (10.7–838.9) |
| Below 100% of the FPL | 0.056 (0–1) |
| Between 100% and 150% of the FPL | 0.100 (0–1) |
| Between 150% and 200% of the FPL | 0.104 (0–1) |
| Above 200% of the FPL | 0.740 (0–1) |
| WASI | |
| Full-scale IQ | 112 (75–160) |
| Performance IQ | 111 (72–157) |
| Verbal IQ | 110.4 (73–156) |
| WJ-III | |
| Math computation | 110.3 (74–156) |
| Letter-word identification | 108.6 (71–151) |
| Passage comprehension | 107.7 (71–140) |
Abbreviations: FPL, federal poverty level; WASI, Wechsler Abbreviated Scale of Intelligence; WJ-III, Woodcock-Johnson III Tests of Achievement.
Analysis sample comprised 823 observations of 389 children with neuroimaging and sociodemographic information. Family income assigned the value of the categorical midpoint. Household income levels were overwhelmingly stable across the sample period, with very few families observed to transition into or out of poverty. Mean (SD) scores on both the WASI and WJ-III were standardized (100 [15]). The WASI and WJ-III batteries were administered to children who were aged at least 5 and 6 years, respectively.