Combining criteria with AND shrinks a category while OR expands it

Evidence

Clearly, if we add attributes with AND the extension can only go down (or remain the same in exceptional circumstances). However, if we use OR to add dimensions then the extension almost certainly goes up. This is visible if one imagines Venn diagrams; the intersection of two sets (representing two attributes) is almost always smaller than either set individually. In contrast, the union is almost always larger than the individual sets. — Gary Goertz, Social Science Concepts and Measurement, 1418

Categorization

• XREF: Connects to any coding or rubric work: adding mandatory criteria versus accepting any-of criteria mechanically moves who gets included.
• DEFINE: Gives concrete operational meaning to ‘intension up, extension down’ via set intersection and union.