From the announcement:

The Guy Medal in Bronze is awarded to Peng Ding for his methodological and theoretical contributions to causal inference, specifically for his three papers in JRSS B: Ding and Lu (2017), Jiang, Ding and Geng (2016) and Ding, Feller and Miratrix (2016).  Despite only having been awarded his PhD in 2015, his work in these three papers provides a ground-breaking theoretical foundation for conducting objective causal inference.