Table 6. Summary of substance abuse-related papers.

Data source	SML a	UML b	CML c	MML d	Surv e	HC f	Senti g	Lexicon h
Reddit	-	[11-13]	[11-13]	-	12	-	-	13
Twitter	[6, 36, 40, 45-49]	[6, 1 2, 35,37, 39, 41, 42, 43, 45]	[6, 12, 35, 36, 38-43, 45-49]	[6, 37]	[1 1, 12, 35, 36, 38, 39, 42, 44, 47-49]	43	[46-48]	44
OHC i	-	[12, 13]	[12, 13]	-	12	-	-	13

^aSupervised machine learning;

^bUnsupervised machine learning;

^cClassical machine learning;

^dModern machine learning;

^eSurveillance;

^fHealth communication;

^gSentiment analysis;

^hLexicon;

ⁱOnline Health Communities