TABLE 1

Demographic and Clinical Characteristics of Subjects and Observations

Subjects, n (%)Observations, n (%)
Met inclusion criteria78 314435 487
    Excluded because head circumference was physiologically implausible or likely erroneous36 subjects whose only observations excluded2043 (0.5)
    Excluded because birth weight was <1500 g285917 803(4.1)
    Excluded because observation was at <3 d of age7 subjects whose only observations were before 3 d of age183 (0.04)
Included in primary analysis
    Total75 412415 458
    Male38 677(51.3)212 836(51.2)
    Female36 735(48.7)202 609(48.8)
    American Indian, Eskimo, or Alaska Native100 (0.1)547 (0.1)
    Asian2142 (2.8)11 467(2.8)
    Black/African American25 263(34)137 102(33)
    Native Hawaiian or Pacific Islander15 (0.02)101 (0.02)
    Other10 445(14)55 102(13)
    Refused9 (0.01)43 (0.01)
    White37 438(50)211 083(51)
    Hispanic2393 (3.2)12 302(2.7)
    Mean No. of observations per subject5.5
Excluded for additional analyses
    Subject ever had ICD-9 code for pathologic condition that can cause abnormal head size2069 (3)12 480(3.0)
    Subject with a gestational age of 33–36 wk2462 (3)15 216(4)
    Observations taken at visit with billing code for sick visit18 348(4)
  • ICD-9 indicates International Classification of Diseases, Ninth Revision.