## Probability Distributions

It's beyond the scope of this book to delve into probability distributions and calculations, so I'll point out a few aspects of them that you should remember for the exam.

Continuous probability distributions (particularly beta and triangular distributions) are commonly used in Perform Quantitative Risk Analysis. According to the PMBOKĀ® Guide, continuous probability distributions include normal, lognormal, triangular, beta, and uniform distributions. Distributions are graphically displayed and represent both the probability and time or cost elements.

Triangular distributions use estimates based on the three-point estimate (the pessimistic, most likely, and optimistic values). This means that during your interviews, you'll gather these pieces of information from your experts. Then you'll use them to quantify risk for each WBS element.

Normal and lognormal distributions use mean and standard deviations to quantify risk, which also require gathering the optimistic, most likely, and pessimistic estimates.

Discrete distributions represent possible scenarios in a decision tree (we'll discuss this in the next section), outcomes of a test, results of a prototype, and other uncertain events.