Proper statistical analysis of planned fatigue experiments involves writing the mathematical model relevant to the given organizational structure (for example, a split plot program), transforming the observed data as required (for example, taking log life), performing the appropriate statistical analysis pertinent to the stated test objective, and examining the residual errors to ascertain as well as possible whether the transformed data meet the assumptions underlying the mathematical model and analysis. This overall process is mandatory for all fatigue test programs, even though the individual steps may differ considerably in their detail and rigor depending on the situation.