Choosing negative cases to test a theory lacks clear rules.

Evidence

Nor did she choose to analyze Canada in 1890, Australia in 1950, or most of the millions of non–social revolutions that have occurred in world history. Instead, she selected a sample of “negative cases” that she regarded as relevant and appropriate for testing her theory of social revolution. In qualitative research, most analysts must—like Skocpol—select a set of negative cases to test their theories. However, the rules for choosing and justifying a set of cases defined by the occurrence of a nonevent are far from straightforward. — Gary Goertz, Social Science Concepts, 1101

Categorization

• QUESTION: What would a defensible rule for selecting non-events look like — random sampling of the null set, or matched structural analogues?