WHEN DOES A STATE BECOME A ‘‘NUCLEAR WEAPON STATE’’? An Exercise in Measurement Validation

When does a state become a ‘‘nuclear weapon state’’? How we choose to answer this question has significant implications for proliferation assessment, analysis, and policy. Traditionally, the standard demarcation line has been a state’s first nuclear test, but in recent years analysts have increasingly focused instead on the accumulation of a significant quantity (SQ) of fissile material. The article argues that although the test/no-test indicator clearly has problems, its replacement by the SQ/no-SQ indicator would be highly counterproductive. The article instead proposes supplementing the traditional test/no-test indicator with a theory-driven approach that focuses on the incentives and disincentives to test.