More Like this

1. Almost-Matching-Exactly for Treatment Effect Estimation under Network Interference

   Awan, Usaid; Morucci, Marco; Orlandi, Vittorio; Roy, Sudeepa; Rudin, Cynthia; Volfovsky, Alexander (January 2020, Proceedings of the Twenty Third International Conference on Artificial Intelligence and Statistics)

   null (Ed.)

   We propose a matching method that recovers direct treatment effects from randomized experiments where units are connected in an observed network, and units that share edges can potentially influence each others’ outcomes. Traditional treatment effect estimators for randomized experiments are biased and error prone in this setting. Our method matches units almost exactly on counts of unique subgraphs within their neighborhood graphs. The matches that we construct are interpretable and high-quality. Our method can be extended easily to accommodate additional unit-level covariate information. We show empirically that our method performs better than other existing methodologies for this problem, while producing meaningful, interpretable results. 

   more » « less
2. Self-relevance effects and label choice: Strong variations in label-matching performance due to non-self-relevant factors

   https://doi.org/10.3758/s13414-017-1307-8  

   Wade, Gregory L.; Vickery, Timothy J. (April 2017, Attention, Perception, & Psychophysics)

   Merely associating one’s self with a stimulus may be enough to enhance performance in a label-matching paradigm (Sui, He, & Humphreys, 2012), implying prioritized processing of self-relevant stimuli. For instance, labeling a square as SELF and a circle as OTHER yields speeded performance when verifying square-SELF compared with circle-OTHER label matches. The precise causes of such effects are unclear. We propose that prioritized processing of label-matches can occur for reasons other than self-relevance. Here, we employ the label-matching paradigm to show similar benefits for non-self-relevant labels (SNAKE, FROG, and GREG) over a frequently employed, non-self-relevant control label (OTHER). These benefits suggest the possibility that self-relevance effects in the label-matching paradigm may be confounded with other properties of labels that lead to relative performance benefits, such as concreteness. The size of self-relevance effects may be overestimated in prior work employing the label-matching paradigm, which calls for greater care in the choice of control labels to determine the true magnitude of self-relevance effects. Our results additionally indicate the possibility of a powerful effect of concreteness (and related properties) on associative memory performance. 

   more » « less
3. Is It Who You Are or Where You Are? Accounting for Compositional Differences in Cross-Site Treatment Effect Variation

   https://doi.org/10.3102/10769986231155427  

   Lu, Benjamin; Ben-Michael, Eli; Feller, Avi; Miratrix, Luke (August 2023, Journal of Educational and Behavioral Statistics)

   In multisite trials, learning about treatment effect variation across sites is critical for understanding where and for whom a program works. Unadjusted comparisons, however, capture “compositional” differences in the distributions of unit-level features as well as “contextual” differences in site-level features, including possible differences in program implementation. Our goal in this article is to adjust site-level estimates for differences in the distribution of observed unit-level features: If we can reweight (or “transport”) each site to have a common distribution of observed unit-level covariates, the remaining treatment effect variation captures contextual and unobserved compositional differences across sites. This allows us to make apples-to-apples comparisons across sites, parceling out the amount of cross-site effect variation explained by systematic differences in populations served. In this article, we develop a framework for transporting effects using approximate balancing weights, where the weights are chosen to directly optimize unit-level covariate balance between each site and the common target distribution. We first develop our approach for the general setting of transporting the effect of a single-site trial. We then extend our method to multisite trials, assess its performance via simulation, and use it to analyze a series of multisite trials of adult education and vocational training programs. In our application, we find that distributional differences are potentially masking cross-site variation. Our method is available in the balancer R package. 

   more » « less
4. Design Considerations and Robustness to Parameter Uncertainty in Wire-Wrapped Cam Mechanisms

   https://doi.org/10.1115/1.4056600  

   Johnston, Garrison L.; Orekhov, Andrew L.; Simaan, Nabil (February 2024, Journal of Mechanisms and Robotics)

   Abstract Collaborative robots must simultaneously be safe enough to operate in close proximity to human operators and powerful enough to assist users in industrial tasks such as lifting heavy equipment. The requirement for safety necessitates that collaborative robots are designed with low-powered actuators. However, some industrial tasks may require the robot to have high payload capacity and/or long reach. For collaborative robot designs to be successful, they must find ways of addressing these conflicting design requirements. One promising strategy for navigating this tradeoff is through the use of static balancing mechanisms to offset the robot’s self-weight, thus enabling the selection of low-powered actuators. In this paper, we introduce a novel, two degrees-of-freedom static balancing mechanism based on spring-loaded, wire-wrapped cams. We also present an optimization-based cam design method that guarantees the cams stay convex, ensures the springs stay below their extensions limits, and minimizes sensitivity to unmodeled deviations from the nominal spring constant. Additionally, we present a model of the effect of friction between the wire and the cam. Lastly, we show experimentally that the torque generated by the cam mechanism matches the torque predicted in our modeling approach. Our results also suggest that the effects of wire-cam friction are significant for non-circular cams. 

   more » « less
5. Time-division TCP for reconfigurable data center networks

   https://doi.org/10.1145/3544216.3544254  

   Chen, Shawn Shuoshuo; Wang, Weiyang; Canel, Christopher; Seshan, Srinivasan; Snoeren, Alex C.; Steenkiste, Peter (August 2022, Proceedings of the ACM SIGCOMM 2022 Conference)

   Recent proposals for reconfigurable data center networks have shown that providing multiple time-varying paths can improve network capacity and lower physical latency. However, existing TCP variants are ill-suited to utilize available capacity because their congestion control cannot react quickly enough to drastic variations in bandwidth and latency. We present Time-division TCP (TDTCP), a new TCP variant designed for reconfigurable data center networks. TDTCP recognizes that communication in these fabrics happens over a set of paths, each having its own physical characteristics and cross traffic. TDTCP multiplexes each connection across multiple independent congestion states---one for each distinct path---while managing connection-wide tasks in a shared fashion. It leverages network support to receive timely notification of path changes and promptly matches its local view to the current path. We implement TDTCP in the Linux kernel. Results on an emulated network show that TDTCP improves throughput over both traditional TCP variants, such as DCTCP and CUBIC, and multipath TCP by 24--41% without requiring significant in-network buffering to hide path variations. 

   more » « less