Join one of our upcoming courses taking place around the world! Explore now

# Statistical Distributions Overview

Each random variable that you define in RocFall must have a Statistical Distribution selected. The following statistical distributions are available in RocFall:

There are two methods you can use to specify the statistical distributions for random variables: using the pop-up window or using the Statistics dialog.

#### Notes:

• The type of Statistical Distribution, together with the statistical parameters of the distribution (mean, standard deviation, minimum and maximum values), defines a Probability Density Function (PDF) for the random variable.
• The PDF describes the distribution of possible values that the random variable may assume for a hypothetical, infinite set of observations of the variable.
• In most cases, very limited data is available on which to decide what Statistical Distribution and standard deviation to use. Therefore, the engineer must often rely on "best estimates" when defining the PDF for a random variable.

## Normal Distribution

A Normal Distribution is commonly used for statistical analysis in geotechnical engineering. When the true distribution of a variable is not known, a Normal Distribution is often assumed. By making a best estimate of the minimum and maximum values of the variable, a standard deviation can be estimated. This is described in the Normal Distribution topic.

## Other Distributions

Although a Normal Distribution is most commonly used, the user should become familiar with the properties, and advantages of using other Statistical Distributions.