Distributions provide clues about the population from which a sample is drawn. The characteristics or parameters that define a distribution are deduced using inferential statistics. These parameters, which vary from distribution to distribution, describe and influence the behavior of the distribution. For example, while shape factor (β) and characteristic life (η) are the two parameters for the Weibull distribution, mean (μ) and standard deviation (σ parameters) are the two parameters for the normal distribution.

The distributions used to model failure and repair times are described in the following topics: