Mean-reversion in real exchange rates has been observed in previous studies, with deviations from purchasing power parity (PPP) having a half-life of around four years. A new study looked at data from 150 countries over 45 years post-WWII and found strong evidence of mean-reversion in PPP deviations. These deviations decrease by about 15% each year, meaning they have a half-life of approximately four years. This pattern is easier to see in cross-sections of data compared to time-series analysis.