Purchasing power parity
What is Purchasing power parity?
Purchasing power parity, or PPP, links exchange rates to relative price levels so comparable baskets would cost the same after currency conversion under idealized conditions.
PPP comparisons should identify price index, base period, countries, data vintage, and whether the result is an absolute level or relative change. It is a long-horizon analytical anchor, not a precise trading target. Structural productivity, taxes, trade barriers, and nontradable goods can sustain gaps.
Revisions to national price data should remain visible when evaluating historical signals.
Investor conclusions should be stress-tested across alternative baskets, inflation measures, productivity assumptions, and convergence speeds.
Absolute and relative PPP
Absolute PPP compares price levels across countries and implies an equilibrium exchange rate for an equivalent basket. Relative PPP focuses on change, suggesting currencies adjust over time by inflation differences. Both require aligned goods, quality, weights, taxes, and dates. Real-world price indexes are not identical baskets and introduce measurement limits.
Why gaps persist
Transport cost, tariffs, taxes, nontradable services, regulation, productivity, market segmentation, capital flows, risk premia, and price stickiness can sustain deviations. Housing and local services cannot be arbitraged like standardized traded goods. A currency can appear undervalued under one PPP data set and fairly valued under another for years.
Uses
Economists use PPP exchange rates to compare real output and living standards, while investors use valuation gaps and real exchange rates as long-horizon context. PPP can inform scenarios, but short- and medium-term currency returns are dominated by rates, flows, policy, risk, and positioning. Misvaluation is not a reliable timing signal alone.
Example
If a comparable basket costs 100 units in one country and 200 in another, simple absolute PPP implies two second-country currency units per first-country unit. If market rate is three, the first appears expensive by that model. Different income, tax, quality, and nontradable content can explain part of the gap.
Practical interpretation
State basket, source, base year, index, market pair, and whether analysis uses level or inflation change. Use ranges and several models, preserve data vintages, and test convergence horizon. Avoid converting a PPP valuation directly into a forecast return or assuming cheaper local prices make an investable currency riskless.
Also known as: PPP
Sources and further reading
- Currency Exchange Rates: Understanding Equilibrium Value, CFA Institute