Self-preferencing by platforms: A literature review*

We survey the economics literature on dual-role platforms and self-preferencing by them. Existing studies mainly consist of theoretical studies, but there are also some empirical studies. Regardless of whether it is theoretical or empirical, many studies on self-preferencing are concerned with the manipulation of search results and recommendation algorithms. Some recent studies have examined first-party selling by platforms that use proprietary transaction data collected from third-party sellers. However, little has been explored about other types of self-preferencing. Findings reported in the existing literature indicate that the impact of self-preferencing on consumers depends largely on the forms of self-preferencing and market environments, implying that policymakers need to gather relevant information on a case-by-case basis for better decisionmaking. Finally, we discuss the types of data used in existing empirical studies, which suggest what kind of data and information can (not) be accessible by researchers. Several directions for future research are also proposed.