Modern technology innovations feature a successive and even recurrent procedure. Intervals between old and new generations of technology are shrinking, and the Internet and Web services have facilitated the fast adoption of an innovation even before the convergence of its predecessor. While the adoption and diffusion of innovations have been studied for decades, most theories and analyses focus on single and one-time innovations. Meanwhile, limited work has investigated successive innovations while lacking user-level analysis, possibly due to the unavailability of fine-grained adoption behavior data. In this study, we present the first large-scale analysis of the adoption of recurrent innovations in the context of mobile app updates, investigating how millions of users consume various versions of thousands of apps on their mobile devices. Our analysis reveals novel patterns of crowd and individual adoption behaviors, which suggest the need for new categories of adopters to be added on top of the Rogers model of innovation diffusion. We show that standard machine learning models are able to pick up various sources of signals to predict whether users in these different categories will adopt a new version of an app and how soon they will adopt it.

User mobility prediction is widely considered by the research community. Many studies have explored various algorithms to predict where a user is likely to visit based on their contexts and trajectories. Most of existing studies focus on specific targets of predictions. While successful cases are often reported, few discussions have been done on what happens if the prediction targets vary: whether coarser locations are easier to be predicted, and whether predicting the immediate next location on the trajectory is easier than predicting the destination. On the other hand, while spatiotemporal tags and content information are commonly used in current prediction tasks, few have utilized the finer grained, on-device user behavioral data, which are supposed to be more informative and indicative of user intentions. In this paper, we conduct a systematic study on the mobility prediction using a large-scale real-world dataset that contains plentiful contextual information. Based on a series of learning models, including a Markov model, two recurrent neural network models, and a multi-modal learning method, we perform extensive experiments to comprehensively investigate the predictability of different types of granularities of targets and the effectiveness of different types of signals. The results provide insightful knowledge on what can be predicted along with how, which sheds light on the real-world mobility prediction from a relatively general perspective.

To improve app quality and nip the potential threats in the bud, modern app markets have released strict guidelines along with app vetting process before app publishing. However, there has been growing evidence showing the ineffectiveness of app vetting, making potentially harmful and policy-violation apps sneak into the market from time to time. Therefore, app removal is a common practice, and market maintainers have to remove undesired apps from the market periodically in a reactive manner. Although a number of reports and news media have mentioned removed apps, our research community still lacks the comprehensive understanding of the landscape of this kind of apps. To fill the void, in this paper, we present a large-scale and longitudinal study of removed apps in iOS app store. We first make great efforts to record daily snapshot of iOS app store continuously in a span of 1.5 years. By comparing each two consecutive snapshots, we have collected the information of over 1 million removed apps with their accurate removed date. This comprehensive dataset enables us to characterize the overall landscape of removed apps. We observe that, although most of the removed apps are low-quality apps (e.g., outdated and abandoned), a number of the removed apps are quite popular. We further investigate the practical reasons leading to the removal of such popular apps, and observe several interesting reasons, including ranking fraud, fake description, and content issues, etc. More importantly, most of these mis-behaviors can be reflected on app meta information including app description, app review, and ASO keywords. It motivates us to design an automated approach to flagging the removed apps. Experiment result suggests that, even without accessing to the bytecode of mobile apps, we can identify the removed apps with good performance (F1=83%). Furthermore, we are able to flag the removed apps in advance as long as their inappropriate behaviors appear in their metadata. We believe our approach can work as a whistle blower that pinpoints policy-violation behaviors timely, which will be quite effective in improving the app maintenance process.