Is Europe falling behind the US on productivity? The Krugman vs Aghion–Bergeaud–Garicano debate hinges on one choice: current vs constant PPPs. A new note maps the gap behind it — all 27 EU states, two data sources — and what it does and doesn't settle. 🧵 At current PPPs (each year's own price comparison) the EU–US gap barely widens. At constant PPPs (a fixed base year) it widens sharply. They diverge because EU prices fell vs the US by more than the inflation differential implies. That divergence is a puzzle.