In theoretical probability, the distribution of events can be inferred without collecting data. For example, we can compute the probability of getting "heads or tails" on a coin flip without actually flipping the coin. In empirical probability, data must be collected by some process, and the probability that each event will occur must be estimated from the data. In health care research, empirical probability is used when reporting characteristics of a sample (e.g., 35% of the sample was female) and classical probability (e.g., theoretical probability distributions) is used when making statistical inferences about the data