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Population Genetics and Statistics for Forensic Analysts

Logical Approach

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Bayes Theorem

Many statisticians have employed what is known as Bayesian probability, after the British clergyman Thomas Bayes, which is based on probability as a measure of one's degree of belief.01 This type of probability is conditional in that the outcome is based on knowing information about other circumstances and is derived from Bayes Theorem, published in 1764.14

Conditional Probability

Conditional probability, by definition, is the probability P of an event A given that an event B has occurred.15 Mathematically, conditional probabilities can be represented as: P(A | B) where "|" means "given that."


Take the example of a die with six sides. If one was to throw the die, the probability of it landing on any one side would be 1/6. This probability, however, assumes that the die is not weighted or rigged in any way, and that all of the sides contain a different number. If this were not true, then the probability would be conditional and dependent on these other factors.

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Date Created: July 17, 2023