3.1: Introduction

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This chapter deals with how to select a probability distribution to represent a random quantity in a simulation model. As seen in previous examples, random quantities are used to represent operation times, transportation times, and repair times well as the time between the arrival of entities and the time between equipment breakdowns. The type of an entity could be a random quantity, as could the number of units demanded by each customer from a finished goods inventory.

In determining the particular probability distribution function to use to model each random quantity, available data as well as the properties of the quantity being modeled must be taken into account. Estimation of distribution function parameters must be performed.

Frequently, data is not available. Choosing a distribution function in the absence of data is discussed including which distributions are commonly used in this situation. Software based procedures for choosing a distribution function when data is available, including fitting the data to a distribution function, are presented. The probability distributions commonly employed in simulation models are described.