“…The first step in Stage 1 was to determine the search engine. Due to its robustness and broader search scope (Cui et al, 2018; Neto et al, 2016), the Web of Science (WoS) has been widely adopted as the single search engine by previous PPP researchers (Cui et al, 2018; Meng & Lu, 2017; Neto et al, 2016; Petersen, 2019; Torchia et al, 2015; H. M. Wang et al, 2018; Xiong et al, 2019). In addition, the WoS covers the longest timeframe of publications, where the literature can be traced back to 1900 (Falagas, Pitsouni, Malietzis, & Pappas, 2008).…”