Random Effects

Random Effects - Random effects result from factors having levels that are representative of a larger set of levels. An assumption is made that the random levels included in the design are representative because they are chosen randomly from a population having Normally distributed effects. They are included in a design as a non-systematic source of variation. Blocking factors are used as random effect factors. Random factors are often nuisance parameters; they may be a source of variation, but they are generally not useful for control. They are often included in a design with the hope, if not the expectation, that they will be found to be non-significant.