Statistical method can be usefully represented as a series of five
stages - Problem, Plan, Data,
Analysis, Conclusion. We use the acronym PPDAC to refer to this series.
Each stage of statistical method comes with its own issues to be understood
and addressed (summarized in the table of Figure 8).
One stage leads to the next and is dependent on previous stages. Looking back, this means that each stage is carried out and legitimized (or not) in the context of the stages which precede it (e.g. there is little value in a Plan that does not address the Problem; in such a case, one of the two stages must be modified). Looking ahead at any stage, choices can be made that will simplify actions taken in a later stage (e.g. a well designed Plan can simplify the Analysis).
A structure for statistical method is useful in two ways: first to provide a template for actively using empirical investigation and second, to critically review completed studies. The structure of all empirical studies, either implicitly or explicitly, can be represented by the five stage model.
In this section, we expand on the key concepts and tasks of each stage introducing new terminology as needed. Michelson's 1879 investigation will be used as illustration. As pointed out in the first section, in many ways this investigation is not typical of a statistical one and we urge the readers to test the proposed structure and language on other applications.
