Answer: Epidemiology
Step-by-step explanation:
Epidemiology is the study that focuses on health-related distribution model and measures for reducing and managing health-related issues.This study defined about determinants of the disease such as why it is caused, when it is caused, where, who etc.
According to the question,John Snow's research is considered as study of epidemiology because he studies about conditions of diseases along with protective measure.He also studied about determinants and distributive functions of health issues.