Parents who indicated an interest in the study were screened by telephone with regard to sociodemographic characteristics and further eligibility criteria. Initial inclusion criteria required that both parents were cohabiting since the infant's birth, the target infant was the youngest child in the family and did not have any major medical problems, the mother was not pregnant at the time of recruitment, there were no mother-infant separations of over a week's time, and the biological parents were the primary caregivers. These criteria were important to control because each of these has the potential to markedly alter parent-infant interactions. Additional inclusion criteria were utilized to minimize the possibility that any observed infant behaviors could be the result of prenatal exposure to drugs or heavy alcohol use. These additional criteria were that there could be no maternal drug use during pregnancy or the past year except for mild marijuana use (no more than twice during pregnancy), the mother's average daily ethanol consumption was.50 oz or less and she did not engage in binge drinking (5 or more drinks per occasion) during pregnancy.
