Before revision: While epidemiology is "the study of the distribution and determinants of states of health in populations", social epidemiology is "that branch of epidemiology concerned with the way that social structures, institutions, and relationships influence health."
After revision: While epidemiology is "the study of the distribution and determinants of states of health in populations", social epidemiology is "that wood of epidemiology concerned with the way that social structures, institutions, and relationships influence health."