In situations where certainty is not possible, it can be helpful to assess how likely it is that something will occur. Quantification of this likelihood is particularly helpful in statistical analysis. The concept of probability is used in everyday language, but more loosely than in statistics. The statement “I’ll probably be there on Saturday” involves a probabilistic statement, but there is no precise degree of quantification. If you know the individual making this statement, past experience may lead you to an informed judgment concerning the relative meaning of probably, but this is still a subjective judgment, not a quantitative statement.
In statistics, a probability is a numerical quantity between zero (represented here as 0.00) and one (1.00) that expresses the likely occurrence of a future event. Past events cannot be associated with a probability of occurrence, since it is known in absolute terms whether they occurred or not. A probability of zero denotes that the...