The language in which methods are often treated in the literature suggests that they are something technical, nonpsychological, or different than substantive variables. But "method" is a summary concept for a multitude of ways in which we obtain psychological information. The result of a method has psychological significance as does the method itself. Returning to the neighbor example, self-report, other-report, and observation were introduced as methods because the different procedures collected the method's provided data. Yet the data are psychological data and the status of these data is the same for each method. They are indicators of assumed causes (altruistic personality, need for approval, marital satisfaction, sympathy). Methods are sets of causes and different sets (methods) contain different elements (causes). Causes as components of a method do not differ from causes that appear in psychological theories. Both the causes of substantive models and the causal components of methods are hypothetical constructs. Therefore, methods (self-report) can be imbedded in psychological theories like substantive causes (altruistic personality). Moreover, methods not only can be imbedded in psychological theories, they must be imbedded in psychological theories. It follows from this claim that methods must be submitted to construct validation (Cronbach & Meehl, 1955) just like what Campbell and Fiske (1959) termed trait-method units (tests). This view has several important consequences, not seriously treated in the literature thus far. To hint at only two of these consequences: First, designing new methods and improving methods is as much a matter of theory as a matter of craftsmanship. Furthermore, selecting methods for multitrait-multimethod research must rely on assumptions about the causal components of methods. Methods are not the same because they capture the same type of data. Two self-report questionnaires are the same method only to the extent that they share diagnostically irrelevant causal components. In some cases, two self-report questionnaires may share fewer diagnostically irrelevant causal components than a self-report and an other-report questionnaire. If so, the two self-report questionnaires are not the same methods. In fact, they are less similar as methods than the self- and other-report questionnaires.
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