In statistics, a proportion is "a probability - as a measure of the chance that a specified event happens to, or that a specific characteristic is possessed by, a typical member of a population...the terms probability, relative frequency, and proportion are used synonymously."
- Fleiss, Joseph L.; Levin, Bruce R. ;Cho Paik, Myunghee; (2003). Statistical methods for rates and proportions. Hoboken, NJ: J. Wiley-Interscience. ISBN 0-471-52629-0.