All Publications

  • The limits of human predictions of recidivism. Science advances Lin, Z. J., Jung, J. n., Goel, S. n., Skeem, J. n. 2020; 6 (7): eaaz0652


    Dressel and Farid recently found that laypeople were as accurate as statistical algorithms in predicting whether a defendant would reoffend, casting doubt on the value of risk assessment tools in the criminal justice system. We report the results of a replication and extension of Dressel and Farid's experiment. Under conditions similar to the original study, we found nearly identical results, with humans and algorithms performing comparably. However, algorithms beat humans in the three other datasets we examined. The performance gap between humans and algorithms was particularly pronounced when, in a departure from the original study, participants were not provided with immediate feedback on the accuracy of their responses. Algorithms also outperformed humans when the information provided for predictions included an enriched (versus restricted) set of risk factors. These results suggest that algorithms can outperform human predictions of recidivism in ecologically valid settings.

    View details for DOI 10.1126/sciadv.aaz0652

    View details for PubMedID 32110737

    View details for PubMedCentralID PMC7021503

  • I'll Be Back: On the Multiple Lives of Users of a Mobile Activity Tracking Application. Proceedings of the ... International World-Wide Web Conference. International WWW Conference Lin, Z., Althoff, T., Leskovec, J. 2018; 2018: 1501–11


    Mobile health applications that track activities, such as exercise, sleep, and diet, are becoming widely used. While these activity tracking applications have the potential to improve our health, user engagement and retention are critical factors for their success. However, long-term user engagement patterns in real-world activity tracking applications are not yet well understood. Here we study user engagement patterns within a mobile physical activity tracking application consisting of 115 million logged activities taken by over a million users over 31 months. Specifically, we show that over 75% of users return and re-engage with the application after prolonged periods of inactivity, no matter the duration of the inactivity. We find a surprising result that the re-engagement usage patterns resemble those of the start of the initial engagement period, rather than being a simple continuation of the end of the initial engagement period. This evidence points to a conceptual model of multiple lives of user engagement, extending the prevalent single life view of user activity. We demonstrate that these multiple lives occur because the users have a variety of different primary intents or goals for using the app. These primary intents are associated with how long each life lasts and how likely the user is to re-engage for a new life. We find evidence for users being more likely to stop using the app once they achieved their primary intent or goal (e.g., weight loss). However, these users might return once their original intent resurfaces (e.g., wanting to lose newly gained weight). We discuss implications of the multiple life paradigm and propose a novel prediction task of predicting the number of lives of a user. Based on insights developed in this work, including a marker of improved primary intent performance, our prediction models achieve 71% ROC AUC. Overall, our research has implications for modeling user re-engagement in health activity tracking applications and has consequences for how notifications, recommendations as well as gamification can be used to increase engagement.

    View details for PubMedID 29780978

  • Quantifying and Predicting Mental Illness Severity in Online Pro-Eating Disorder Communities Chancellor, S., Lin, Z., Goodman, E. L., Zerwas, S., De Choudhury, M., ACM ASSOC COMPUTING MACHINERY. 2016: 1171–84
  • "This Post Will Just Get Taken Down": Characterizing Removed Pro-Eating Disorder Social Media Content Chancellor, S., Lin, Z., De Choudhury, M., ACM ASSOC COMPUTING MACHINERY. 2016: 1157–62
  • GLO-STIX: Graph-Level Operations for Specifying Techniques and Interactive eXploration IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS Stolper, C. D., Kahng, M., Lin, Z., Foerster, F., Goel, A., Stasko, J., Chau, D. 2014; 20 (12): 2320–28


    The field of graph visualization has produced a wealth of visualization techniques for accomplishing a variety of analysis tasks. Therefore analysts often rely on a suite of different techniques, and visual graph analysis application builders strive to provide this breadth of techniques. To provide a holistic model for specifying network visualization techniques (as opposed to considering each technique in isolation) we present the Graph-Level Operations (GLO) model. We describe a method for identifying GLOs and apply it to identify five classes of GLOs, which can be flexibly combined to re-create six canonical graph visualization techniques. We discuss advantages of the GLO model, including potentially discovering new, effective network visualization techniques and easing the engineering challenges of building multi-technique graph visualization applications. Finally, we implement the GLOs that we identified into the GLO-STIX prototype system that enables an analyst to interactively explore a graph by applying GLOs.

    View details for DOI 10.1109/TVCG.2014.2346444

    View details for Web of Science ID 000344991700077

    View details for PubMedID 26356946

  • MMap: Fast Billion-Scale Graph Computation on a PC via Memory Mapping Lin, Z., Kahng, M., Sabrin, K., Chau, D., Lee, H., Kang, U., IEEE, Lin, J., Hu, X. H., Chang, W., Nambiar, R., Aggarwal, C., Cercone, N., Honavar, Huan, J., Mobasher, B., Pyne, S. IEEE. 2014: 159–64


    Graph computation approaches such as GraphChi and TurboGraph recently demonstrated that a single PC can perform efficient computation on billion-node graphs. To achieve high speed and scalability, they often need sophisticated data structures and memory management strategies. We propose a minimalist approach that forgoes such requirements, by leveraging the fundamental memory mapping (MMap) capability found on operating systems. We contribute: (1) a new insight that MMap is a viable technique for creating fast and scalable graph algorithms that surpasses some of the best techniques; (2) the design and implementation of popular graph algorithms for billion-scale graphs with little code, thanks to memory mapping; (3) extensive experiments on real graphs, including the 6.6 billion edge YahooWeb graph, and show that this new approach is significantly faster or comparable to the highly-optimized methods (e.g., 9.5× faster than GraphChi for computing PageRank on 1.47B edge Twitter graph). We believe our work provides a new direction in the design and development of scalable algorithms. Our packaged code is available at

    View details for Web of Science ID 000380462900024

    View details for PubMedID 25866846

    View details for PubMedCentralID PMC4389765

  • Towards Scalable Graph Computation on Mobile Devices 2014 IEEE INTERNATIONAL CONFERENCE ON BIG DATA (BIG DATA) Chen, Y., Lin, Z., Pienta, R., Kahng, M., Chau, D. H. 2014


    Mobile devices have become increasingly central to our everyday activities, due to their portability, multi-touch capabilities, and ever-improving computational power. Such attractive features have spurred research interest in leveraging mobile devices for computation. We explore a novel approach that aims to use a single mobile device to perform scalable graph computation on large graphs that do not fit in the device's limited main memory, opening up the possibility of performing on-device analysis of large datasets, without relying on the cloud. Based on the familiar memory mapping capability provided by today's mobile operating systems, our approach to scale up computation is powerful and intentionally kept simple to maximize its applicability across the iOS and Android platforms. Our experiments demonstrate that an iPad mini can perform fast computation on large real graphs with as many as 272 million edges (Google+ social graph), at a speed that is only a few times slower than a 13″ Macbook Pro. Through creating a real world iOS app with this technique, we demonstrate the strong potential application for scalable graph computation on a single mobile device using our approach.

    View details for Web of Science ID 000380462900150

    View details for PubMedID 25859564

    View details for PubMedCentralID PMC4388237

  • Leveraging Memory Mapping for Fast and Scalable Graph Computation on a PC Lin, Z., Chau, D., Kang, U., Hu, Lin, T. Y., Raghavan, Wah, B., BaezaYates, R., Fox, G., Shahabi, C., Smith, M., Yang, Q., Ghani, R., Fan, W., Lempel, R., Nambiar, R. IEEE. 2013
  • Demonstrating Interactive Multi-resolution Large Graph Exploration Lin, Z., Cao, N., Tong, H., Wang, F., Kang, U., Chau, D., Ding, W., Washio, T., Xiong, H., Karypis, G., Thuraisingham, B., Cook, D., Wu IEEE. 2013: 1097–1100