What’s the best way to measure economic well-being in a country as large and diverse as America? One crucial tool is price indexes, which allow us to take common measures of flourishing—hourly earnings, median household income, poverty, gross domestic product and productivity—and remove the impact of inflation to allow meaningful comparisons across time periods.

Yet the economists, statisticians and agencies that create price indexes overwhelmingly agree that official measures of inflation are significantly overstated, leading...