John's research expertise includes clinical, molecular, and genetic epidemiology methods. Clinical epidemiology covers such topics as population- and hospital-based observational studies (cohort, case-control, crossover) and controlled clinical trials as well as studies of diagnostic tests, meta-analyses, and health services research. Molecular epidemiology focuses mainly on evaluation of biomarkers. Genetic epidemiology covers design and analysis of genome-wide association studies of various complex diseases, particularly macular degeneration and stroke.