Comparability
For 2017 samples, the universe for this variable includes only infants under age 2 whose survey responses were provided by their biological mother, and who had ever been breastfed by their biological mother.
For 2018 samples, the universe for this question was expanded to include all infants under age 2, including those whose survey responses were provided by their primary caretaker. In some cases, this caretaker is not the infant's biological mother (see RELATEKID).
