Theory-Testing with Cases

Two Types of Proposition

There are two types of proposition: (1) about characteristics of single cases and (2) about differences between cases.

Theory-Testing Single Case Study

Many theories have the form “X results in Y,” or “X contributes to Y,” or “X affects Y,” and so on, in which X is, for example, something that an actor can or cannot do (or a situation or occasion or event that can occur or not occur) and Y is the desired outcome of that action. There are two fundamentally different ways of interpreting such a theoretical statement. Usually, it is meant as a statement that explains differences between cases in the value of one (dependent) variable, Y, by relating them to differences in the values of another (independent) variable, X: “If there is more X, then there is more Y.” Often, however, such a statement is meant to identify X as an important (“critical” or “crucial”) condition that should be present in order to make Outcome Y possible. The intended meaning is that Y is very unlikely to occur if X is absent or, in other words, that Y normally is not possible without the presence of X. This is a necessary condition hypothesis (“Y only if X”). The presence of the necessary condition means that the outcome has become possible, but it does not guarantee that the outcome will occur (which would imply that the condition is sufficient). The concept of a necessary condition must not be confused with a sufficient condition.

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