🔎 The Problem: GDP Masks What States Can Use for Arms
Scholars routinely use gross domestic product (GDP) as a proxy for the income states can devote to arming, but this approach systematically mismeasures power resources. GDP conflates two conceptually distinct forms of income into one additive indicator: subsistence income (the "bread" needed to cover basic population needs) and surplus income (the remaining resources that could be allocated to "guns" or "butter").
📊 What the New Measure Does: Surplus Domestic Product (SDP)
Surplus Domestic Product (SDP) corrects this measurement error by decomposing subsistence income and surplus income from total GDP. SDP isolates the portion of national income that is available for discretionary allocations—such as military spending—rather than treating all GDP as equally fungible for arming.
📑 How SDP Was Evaluated: Validation Exercises and Empirical Models
- Validation exercises compare SDP against GDP in capturing the distribution of power resources and show that SDP outperforms GDP for this purpose.
- Theoretical expectations hold that states' decisions to arm are shaped by the distribution of power resources.
- Empirical models that use GDP find mixed support for this theoretical link; when models substitute SDP for GDP, they reveal strong support for the proposition that distribution of power influences arming decisions.
✅ Key Findings
- GDP conflates necessary subsistence consumption with discretionary surplus and thus mismeasures a state's usable power resources.
- SDP decomposes GDP into subsistence and surplus components, producing a more accurate indicator of resources available for armament.
- Validation exercises show SDP better captures the distribution of power resources than GDP.
- Using SDP in empirical models turns previously mixed evidence into strong support for the theory that resource distribution affects states' decisions to arm.
💡 Why It Matters
Better measurement of available income changes inferences about armament and state behavior. By separating "bread" from "guns or butter," SDP clarifies the resource basis for military burdens and offers a more reliable foundation for research and policy analysis on power, defense spending, and state priorities.
