A research plan must answer four questions: (i) What is the scientific question that the research seeks to answer? (ii) What type of investigation will the researcher conduct? (iii) What measurements will be made? (iv) What type of data analysis will be used, and will there be sufficient statistical power in the data to give an effective answer to the question? I illustrate how each of these questions can be answered. The first requires conceptual and propositional analysis to refine concepts and postulates so that an important scientific question is developed and one that is possible to answer. Questions ii, iii and iv together form a Data Statement that must answer why a particular type of investigation is appropriate and how that question will be answered. It must define the extent to which measurements represent the concepts in question and the accuracy and precision of those measurements. And, most important, the Data Statement must define the type of data analysis that will be used, including a definition of the statistical power necessary to answer the question effectively. The development of a Data Statement will usually involve exploratory analysis of the scientific question to explore the effectiveness of proposed measurements and to enable calculation of a sampling regimen that will provide adequate statistical power.