Why Incumbency Advantage Is Harder to Measure Outside the U.S.

🧭 The Measurement Problem

High rerunning rates among incumbents and the dominance of two major parties in the United States let U.S.-based studies avoid the selection problem of who chooses to run again. In countries where rerunning is uncommon or parties are fluid, applying U.S. methods can produce sample selection bias and produce misleading estimates of incumbency effects.

📌 What Distorts Estimates

• Low rerunning rates among individuals or parties can bias estimates that condition on the pool of repeat candidates.
• Party switching creates a potential disconnect between estimates that focus on parties and those that focus on individual politicians.

🧭 A Clearer Definition

Proposes a definition of incumbency advantage that works across different institutional contexts and permits cross-country comparison: the effect of incumbency for an individual politician on the unconditional probability of winning.

📊 Illustration Using Brazilian Mayoral Elections

• Presents empirical evidence from Brazilian mayoral elections to demonstrate the problems identified above.
• Uses the Brazilian case to show how conventional estimators can misrepresent incumbency effects when rerunning is not widespread or when party switching occurs.

🔑 Why This Matters

• Offers a conceptually consistent incumbency measure that is applicable in diverse electoral systems.
• Clarifies when and why U.S.-derived methods fail, and provides a comparative framework for more accurate estimation of incumbency effects.