Section 45 Probability: Relative Frequency

• Theoretical probability is the expected probability of an event to happen.

• Experimental probability is the estimation of probability based on an event happening in repeated experiments.

• The most popular version of objective probability is frequentist probability

• These probability estimates are based on ‘relative frequencies’.

• Relative frequencies are calculated from a sample, but probabilities relate to a population.

• Relative frequencies provide estimates for probabilities if we have a random sample from the population of interest.

• Random: every member of the population has an equal chance of being selected

• The sampled data are only representative of the population from which they were sampled.

• The weather data are only representative of the location and time of year they were collected.

• Probability estimates depend on the sample size collecting more data improves the probability estimates.

• The sample size n should be large: the larger n is, the better the estimate of probability.