Never in American history has the debate over income inequality so dominated the public square, with Democratic presidential candidates and congressional leaders calling for massive tax increases and federal expenditures to redistribute the nation’s income. Unfortunately, official measures of income inequality, the numbers being debated, are profoundly distorted by what the Census Bureau chooses to count as household income.

The published census data for 2017 portray the top quintile of households as having almost 17 times...