WHAT IS EPIDEMIOLOGY? Epidemiology is the study of the distribution and determinants of health related states or events (including disease), and the application of this study to control diseases and other health problems [1]. It is concerned with stud ying the presence of disease in a community, c or region, and can help to ascertain the size, severity, spread and origin of a particular disease An epidemiologist deals with diseases in groups of people (whereas a clinician deals with disease in individuals). From epidemiological stud- ies, decisions can be made on the allocation or targeting of resources in a population. Epidemiology is the foundation upon which governments and local authori- ties plan preventive measures for future generations, including oral health, such as the fluoridation of water and how many dentists will need to be trained in 20 or 30 years time to meet demand. The oral health educator (OHE) needs to know how dental surveys are used in epidemiology, as well as indices, which are used to measure data in populations and individuals. Basic Guide to Oral Health Education and Promotion, Second Edition. Ann Felton, Alison Chapman