Search of PubMed—last performed 4 June 2018
#1	infant (n = 1,119,189)
#2	infants (n = 1,159,867)
#3	preterm (n = 62,246)
#4	premature (n = 170,785)
#5	pain (n = 733,273)
#6	relief (n = 84,761)
#6	acupuncture (n = 28,139)
#7	skin-to-skin care (n = 47,999)
#8	non-nutritive sucking (n = 367)
#9	sucrose (n = 74,579)
#10	massage (n = 13,982)
#11	music (n = 22,562)
#12	breastfeeding (n = 49,518)
#13	non-pharmacological (n = 6513)
Search of Google Scholar—last performed 4 June 2018
#1	infant (n = 3,220,000)
#2	infants (n = 2,080,000)
#3	preterm (n = 1,010,000)
#4	premature (n = 2,840,000)
#5	pain (n = 3,770,000)
#6	relief (n = 2,390,000)
#6	acupuncture (n = 592,000)
#7	skin-to-skin care (n = 3,820,000)
#8	non-nutritive sucking (n = 21,900)
#9	sucrose (n = 2,640,000)
#10	massage (n = 773,000)
#11	music (n = 3,770,000)
#12	breastfeeding (n = 649,000)
#13	non-pharmacological (n = 2,540,000)