“…Second, we identify current research trends, main challenges and potential future directions worthy of further explorations. This review complements review articles recently published on users' responses (including CTR, conversion rate and user engagement) prediction (Gharibshah and Zhu, 2021) and CTR prediction (Wang, 2020;Zhang et al, 2021a). More specifically, Gharibshah and Zhu (2021) focused on online advertising platforms, data sources and features, and typical methods for user response prediction; Wang (2020) briefly introduced several classical methods for CTR prediction; and Zhang et al (2021a) concentrated on the transfer from shallow to deep learning models for CTR prediction, explicit feature interaction modules and automated methods for architecture design.…”