Definition:Relative Frequency Model

Definition
The Relative Frequency model is a measure that defines the probability of an event occurring as follows:


 * $\Pr\left(\text{event occurring}\right) := \dfrac {\left( \text {observed number of times event has occurred in the past}\right)}{\left( \text{observed number of times event has occurred or not occurred}\right)}$

That is, the probability of an event happening is defined as the relative frequency of events of a particular type in some reference class of events.

Some sources adopt a slightly different definition as a limit that such a frequency converges to, were the number of observations to approach infinity.

Either way, the assumption is that were we to conduct a large number of trials, the frequency of events occurring in the new experiments should be roughly equal to the frequency of events occurring in the observed cases.

Proof that the Relative Frequency model is indeed a probability measure is given here.

Also see

 * Relative Frequency is a Probability Measure
 * Classical Probability