Aggregation choices that boost necessity findings undercut sufficiency findings

Evidence

Our analysis provides substantial support for Skocpol’s theory, though it also raises some lingering questions about specific cases. Above all, the example shows how challenging it is to confirm a twolevel theory that proposes, at the basic level, a set of variables that are individually necessary and jointly sufficient. This is true because an aggregation procedure for moving from secondary-level variables to basic-level causes that makes it more likely to find necessity for individual variables simultaneously makes it more difficult to find sufficiency for a combination of these variables. For example, the maximum will produce high values for the basic-level causes, which in turn will make it easier to find causal necessity when these variables are tested with fuzzy-set methods. At the same time, however, the use of the maximum for constructing basic-level causes will make it more challenging to support claims that these variables are jointly sufficient, since this mode will inflate the value of the causal combination. — Gary Goertz, Social Science Concepts, 1754

Categorization

• DEEPTHINKING: A genuine structural tradeoff: necessity and sufficiency are not independently testable once you commit to an aggregation rule across levels of a theory, which quietly reshapes what evidence can even count.