incidence - the number of new cases of a disease or condition over a given time period. It is the rate at which new cases occur in a defined population group (e.g., the incidence rate of lung cancer is 2.5% per year in 25- to 29-year-old Hispanic males in the US). This term is frequently confused with and used interchangeably in error with the term prevalence which describes how common a disease is. In epidemiology of dental caries, it is important to note the denominator – people or individual teeth.

index - a standard numerical measure of a disease or condition. It extends from the proportion of individuals with a disease or condition to the number of millimeters of probing depth around a tooth. Common indices in dentistry are the DMF Index, which is a measure of caries, the O’Leary Plaque Index, which measures plaque/oral hygiene, and PSR (periodontal screening and report), which indicates treatment need for periodontal therapy.

mean - the arithmetical average, a measure of central tendency together with the measures of mode (the most commonly occured value) and median (the value in an order of numbers that is the midpoint – there are as many values above as below).

NHANES - National Health and Nutrition Examination Survey (NHANES) is a survey conducted by the US National Center for Health Statistics, part of the Centers for Disease Control & Prevention (commonly referred to as CDC), which investigates and publishes reports on the health and nutritional status of Americans. Currently, approximately 5000 people are examined each year.

prevalence - the proportion (%) of individuals exhibiting the disease or condition (e.g., dental caries, TB, lung cancer) in a defined population group (e.g., the prevalence of dental caries is 50% in children aged 6 to 11 years). This term is frequently confused with and used interchangeably in error with another term incidence which reports on the occurrence of new disease cases.