ABSTRACT
The process models analyzed in Chapters 4 and 5 have one thing in common: they assume that activity times and demand are deterministic and constant, that is, that they are known with certainty. In reality, an element of variability will always exist in the time it takes to perform a certain task and in the demand for service. In situations where the variability is small, deterministic models of the type studied in Chapters 4 and 5 might be an adequate way of describing a process. However, in situations with more accentuated variability, these models do not suffice. In fact, the variability itself is often one of the most important characteristics to capture in the model of a process.
