Table 1.

Definition of infant feeding modes in the Infant Feeding Practice Study (IFPSII) questionnaire^a (n = 1899 with valid answers)

Mode of feeding	Does your baby usually feed from both breasts at each feeding? (Question N56)b	Does your baby usually let go of the breast him or herself? (Question N57)	How many times in the past 7 days was your baby fed expressed or pumped breast milk to drink? (Question N61)	In the past 7 days, how often was your baby fed each food listed below? (Question N40a): Breastmilk	In the past 7 days, how often was your baby fed each food listed below? (Question N40b): Formula	Month 1
						n	Total
Formula feeding (FF)	Instructed to skip if not breastfeeding		Instructed to skip	= 0	≥ 1	508	508
			0		≥ 1	0
Pumping & feeding (P&F) combined with formula feeding (FF)	Valid answer	Missing	≥ 1	> 0	≥ 1	61	70
	Valid answer	Missing	0		≥ 1	9
Pumping and feeding (P&F)	Baby is fed only pumped milk	Skipped after n 56	≥ 1	> 0	0	18	18
Pumping & feeding (P&F) combined with direct breastfeeding (DBF)	Valid answer	No	≥ 1	> 0	0	53	341
	Valid answer	Yes	≥ 1		0	285
	Valid answer	Missing	≥ 1		0	3
Direct breastfeeding (DBF)	Valid answer	No	0	> 0	0	56	457
	Valid answer	Yes	0		0	398
	Valid answer	Missing	0		0	3
Direct breastfeeding (DBF) and formula feeding (FF)	Valid answer	No	0	> 0	≥ 1	42	233
	Valid answer	Yes	0		≥ 1	190
	Valid answer	Missing	0		≥ 1	1
Mixed: direct breastfeeding (DBF), Pumping & feeding (P&F), formula feeding (FF)	Valid answer	Yes	≥ 1	> 0	≥ 1	224	272
	Valid answer	Missing	≥ 1		≥ 1	3
	Valid answer	No	≥ 1	> 0	≥ 1	45

^a The questionnaires used in the IFPSII can be assessed at https://www.cdc.gov/breastfeeding/data/ifps/questionnaires.htm

^b The numbers (e.g., n 56) refer to the numbering of the questions in the publicly available data-set