Wide-ranging research interests span all areas of systematic review and meta-analysis. Julian has co-authored more than 60 applied systematic reviews and over 150 papers on methodology. Among his methods contributions are: a Bayesian approach to network meta-analysis; the I-squared statistic to quantify inconsistency across studies in a meta-analysis; simple prediction intervals for random-effects meta-analysis; a general framework for individual participant data meta-analysis; a library of prior distributions for between-study variation in a meta-analysis; and risk-of-bias assessment tools for clinical trials and other study designs. He was a member of the development teams for the original PRISMA reporting guideline for systematic reviews and meta-analyses and the STROBE-MR reporting guidelines for Mendelian randomization studies, and co-led development of the STREGA reporting guideline for genetic association studies.