Table 2.

Included papers, main outcomes, and the effect on either brand trust, message credibility, or source credibility (including trustworthiness, believability, and competence) as specified in their results.

Factors		Platform	Population	Outcome	Resulta	Relevant papers
Language useb
	Gain-framed language
		Facebook	Student	Message credibilityb,c	Increase	Borah and Xiao [47]
	Personalized language
		Twitter	Student	Competence and trustworthiness	Decrease	Yilmaz and Johnson [59]
		Facebook	Student	Competence and trustworthiness	Increase	Yilmaz and Johnson [59]
	Exposure to civil discussion
		Facebook	Student	Trustworthiness	Increase	Antoci et al [67]
	Nonopinionated language
		Twitter	Paid worker	Message credibility	Increase	Houston et al [51]
		YouTube	Student	Message credibility	No effect	Zimmermann and Jucks [68]
Bandwagon heuristicsb
	High number of likes
		Facebook	Student	Source credibility and trustworthiness	No effect	Borah and Xiao [47]
			Student	Brand trust	Increase	Phua and Ahn [66]
	High number of followers
		Facebook	Student	Believability	Increase	Lee [49]
		Twitter	Student	Source credibility	Westerman and Spence: unclear; Phua and Ahn: increase	Westerman and Spence [57]; Phua and Ahn [66]
	Narrow ratio of the number of followers to the number of follows
		Twitter	Student	Competency	Increase	Westerman and Spence [57]
	High number of retweets
		Twitter	Student	Trustworthiness	Decrease	Lin and Spence [63-65]
	High number of friends
		Facebook	Student	Believability and trustworthiness	Increase	Lee [49]
Expertise heuristicb
	Post from expert source	Facebook and Twitter	Student	Source credibility	Increase	Borah and Xiao [47]; Lin and Spence [63,65]
Otherb
	Interaction with followers	Twitter	Student	Source credibility	Increase	Jahng and Littau [62]
	High perceived privacy control	Facebook	Student	Trust	Increase	Antoci et al [67]
	Positive brand attitude	Instagram	Paid worker	Brand credibility	Increase	De Veirman and Hudders [52]; Jin and Muqaddam [55]
	Prosocial attitude online	Twitter	Student	Source credibility	Increase	Jin and Phua [48]
	Recency of updates (frequent)	Twitter	Student	Source credibility	Increase	Westerman and Spence [56]
	Snapshot aesthetic (vs studio aesthetic)	Instagram	Paid worker	Brand credibility	Increase	Colliander and Marder [54]
	Preexisting photoshop/internet skills (when looking at photoshopped images)	Twitter and Facebook	Paid worker	Source credibility	Decrease	Shen et al [50]
	Ethos message appeal (compared with logos and pathos)	YouTube	Student	Source credibility	Increase	English et al [61]
	Consumer-generated advertising (compared with firm-generated advertising)	YouTube	Student	Source credibility	Increase	Lee et al [69]
	Caucasian ethnicity (compared with African American)	Facebook	Student	Source credibility	Increase	Spence et al [58]

^aOn the basis of reported results from studies summarized in Multimedia Appendices 3-7.

^bFor further context, explanation, and examples of these factors, refer to Multimedia Appendices 3-7.

^cCredibility comprises trustworthiness, expertise, and sometimes attractiveness, depending on the individual paper.