ABSTRACT
This chapter covers the basic concepts of probability: what a probability value means, and how to calculate and combine probabilities. It also explores conditional probabilities, which readers commonly use, but often fail to understand: conditional probabilities are vital to the understanding of all statistical tests most commonly used by biologists. Every probability can be thought of as the probability of a certain event occurring; that is, turning out to be an accurate description of what actually happens. Sometimes the quickest way to calculate a probability is to think of all the possible outcomes, and simply count the proportion for which the event in question occurs. A probability tree is a good way of considering the probability of different events when the overall result depends upon a combination of different outcomes. Finally, the chapter looks at the concept of probability distribution functions, including two distributions that are frequently used to describe events in the biological world: the normal and binomial distributions.
