Statistical analyses
REGRESSION
Baseline characteristics of eligible families and infants are described using percentages for categorical characteristics and means (standard deviations) for continuous characteristics. Associations between demographic characteristics of those approached vs. not approached, and between those who were approached and enrolled vs. refused enrollment, are tested using chi-square tests for categorical characteristics and t-tests for continuous characteristics. The enrollment process over the study period is described through the cumulative number eligible and cumulative number approached, and approach rates are compared between study epochs through chi-square tests. Multiple logistic regression is used to compare both approach and consent rates across study epochs, controlling for characteristics found to be associated with being approached in earlier analyses, which included maternal race/ethnicity for analysis of approach rate, and maternal race/ethnicity and gestational age at birth for consent rates.