Ratio

Definition

A ratio shows the relative magnitude of one quantity to another, obtained by dividing one quantity by the other. This can be expressed by formula ${ a / b }$, where a is the numerator and b is the denominator. A ratio is dimensionless if these two quantities have the same unit, otherwise the ratio has dimension. In the mathematical meaning of the word, ratio is equivalent to quotient ${ a / b }$, i. e. to division of numbers a (dividend) and b (divisor). If this expression is left unevaluated, it is called a fraction.

Examples of ratios include odds-ratio and risk ratio. A specific type of ratio is proportion, in which the numerator is part of the denominator, and with restricted values between 0.0 and 1.0. Proportion is equivalent to a proper fraction. Rate is a type of ratio, in which the numerator is represented by the number of events, and the denominator by the population at risk.