Within- and cross-group spillover effects in influencer marketing: The heterogeneity between micro- and macro-influencers

The meteoric growth of social media has driven firms to leverage influencers in their advertising campaigns, with a preference for those possessing a larger follower base. However, existing research has predominantly examined the role of influencer popularity in isolation, neglecting the interdependencies among influencers within a firm's campaign. In contrast, this study categorizes influencers into two groups—macro- and micro-influencers—based on their popularity, and examines the effect of within- and cross-group spillovers on influencers’ conversion performance. Leveraging data from a real marketing campaign comprising 163 promotional videos of 111 influencers over a 38-month period and utilizing a fixed-effects panel data regression, we found that both within- and cross-group spillovers are significant solely among micro-influencers. Based on these findings, we discuss the theoretical implications for advertising planning and managerial implications for marketing managers seeking to optimize their influencer marketing expenditure.