Introduction

Political decision-making often relies on arbitrary population thresholds to determine local government structures. This article examines how such rules shape municipal governance across different European contexts.

Methods

Using empirical evidence from France, Germany, and Italy, we analyze the application of regression discontinuity designs (RDDs) in policy evaluation studies.

### Key Finding 1: Compound Treatment Effects

When multiple policies change simultaneously at population thresholds, standard RDD approaches may overstate treatment effects.

### Key Finding 2: Sorting Issues

Municipalities strategically position themselves relative to thresholds—a practice that introduces selection bias into traditional estimates.

Implications

Even with these common challenges present:

📍 Population-threshold RDDs remain valuable tools for evaluating certain local governance policies

📍 Researchers must implement specific methods to accurately address sorting and compound treatment issues in their designs