My research interests lie in design and analysis of randomized controlled trials (RCTs), partial identification, identification and inference with multi-valued treatments and instruments, and quantile regression. In one recent paper I study the optimal stratified randomization procedure in RCTs, and found a certain kind of matched-pair design is optimal. In another paper (coauthored with Joe Romano and Azeem Shaikh), we provide asymptotically exact inference procedure for matched-pair designs. In another paper we study inference with moment inequalities whose dimension grows exponentially fast with the sample size. I also have a paper in which we study the sharp identified sets for various treatment effects with multi-valued instruments and multi-values treatments.