Using the same rule to pick cases versus populations yields opposite inclusion errors

Evidence

There is thus a fundamental difference between the way the Possibility Principle is used in the previous chapter and this one. In the case of Skocpol we have the positive cases as defined by the concept of social revolution plus the negative cases determined by the Possibility Principle. In this chapter, we first use the Possibility Principle to determine the population and then use the positive observations that are a subset of that population. In the first procedure (e.g., Skocpol) the impossible cannot happen because the population is the union of the positive and negative cases, hence all positive cases are included. In the second, the impossible can happen because the positive cases are a subset of the population determined by the Possibility Principle. That is the reason why this chapter title refers to “choosing populations”: the Possibility Principle is used to select the population of both positive and negative cases. — Gary Goertz, Social Science Concepts, 1411