Sampling Matrix Geographic RegionEthnicityLength of Time in Program North Caucasian< 18 months (30 families) > 18 months (30 families) African American < 18 months (30 families) > 18 months (30 families) Other< 18 months (30 families) > 18 months (30 families) South Caucasian< 18 months (30 families) > 18 months (30 families) African American < 18 months (30 families) > 18 months (30 families) Other< 18 months (30 families) > 18 months (30 families)
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