  Using tax and census data, we demonstrate that the distribution of individual
income in the USA is exponential. Our calculated Lorenz curve without fitting
parameters and Gini coefficient 1/2 agree well with the data. From the
individual income distribution, we derive the distribution function of income
for families with two earners and show that it also agrees well with the data.
The family data for the period 1947-1994 fit the Lorenz curve and Gini
coefficient 3/8=0.375 calculated for two-earners families.
