A meta-analysis of empirical studies involving more than 31,000 participants has revealed the factors that affect the level of influence of so-called social media influencers. Those factors include credibility, expertise, attractiveness and perceived similarity to their followers. They are, the work shows, positively associated with the attitude of consumers toward the brands mentioned or promoted by those influencers and, in turn, their purchasing intentions. Details of the analysis are published in the International Journal of Internet Marketing and Advertising.