Epidemiology is derived from the Greek term epi, which means on or upon, demos, which means people, and logos, which means study of. To put it another way, epidemiology is the study of what happens to a group of people. Many definitions have been proposed, but the one below best represents epidemiology's fundamental concepts and public health spirit. Epidemiology is the study of the distribution and determinants of health-related states or events in specific populations, as well as the application of this knowledge to the prevention of disease. It is a cornerstone of public health, influencing policy and evidence-based practise by identifying disease risk factors and preventative healthcare priorities. Epidemiologists assist in study planning, data collection, statistical analysis, and interpretation and dissemination. Epidemiology has aided in the development of techniques for clinical research, public health investigations, and, to a lesser extent, basic biological science research.