Understanding probabilities is one of the most important aspects in sports betting. Probability can be defined as the likelihood of a given event’s occurrence or that a statement is true, expressed as a number between 1 and 0 (0%-100%). Mathematically it can be expressed as the number of occurrences divided by the number of occurrence plus the number of failure of occurrences. The sum of probabilities regarding a set of sports event that are collectively and mutually exhaustive must equal 1, meaning that at least one of the possible outcomes will occur at the same time. There are three main types of probabilities:

**Empirical probability**

The empirical probability, also called relative frequency or experimental probability, is the ratio of the number of outcomes to the number of trials. A bettor can assume that if an event has happen x times in the past, it will also happen in the future. The formula is not difficult to understand. For example, if you know that your favorite team won 18 out of 19 home games in the 2012-2013 English Premier league season, you can use the formula and find out that the team will win 94,7% of their home games by dividing 18/19 = 0,947. However, the data from only one season is not enough to draw a viable conclusion about an outcome. This will not happen every season, so a smart bettor must use the formula only when he has sufficient, stable background information or a larger data set.

**A priori probability**

A priori probability is based only on deductive reasoning and is used in distinguishing the ways in which certain values can be acquired. This probability is based on logic and reason. For example, when you flip a coin there is a 50% probability for tail and 50% probability for heads, meaning that the outcomes are equally likely (1.00/2 = 50%).

**Subjective probability**

Subjective probability is the measurement of the likelihood of an outcome based on a someone’s personal viewpoint. Sports bettors can use this method if they do not have any other assessment option available. This probability does not involve any mathematical data and must only be used as a final step in determining an unpredictable outcome. This means that you make up an estimate based on your perception of reality. Many novice bettors end up losing money because they pick bets based on subjective probability. These bettors usually give an event a high probability for their selection.