Relative frequency

Relative frequency rescales a raw count into a fraction or percent, which makes groups of different sizes comparable. For example, if 18 of 40 students walk to school, the relative frequency is $18 / 40 = 0.45$, or 45 percent. The relative frequencies across all categories add up to $1$, that is, 100 percent. This idea is the empirical basis for estimating probabilities from data.