Demographic and FSIQ characteristics of original NIH sample and analyzed sample.

When appropriate, means ± standard deviations are provided.p-values were calculated using the Student's t-test or chi-square test where appropriate.*Based on the US Department of Housing and Urban Development method for comparing family income levels as a function of regional costs of living.**The ‘Other’ category includes American Indian, Alaskan Native, Asian, Native Hawaiian or Other Pacific Islander, and those for which ethnicity or race was not provided or for which parents came from different racial or ethnic background.***WASI IQ data available for only 380 subjects out of 431 that were initially recruited.