They are places where people of similar incomes and ethnic backgrounds meet.
It seems to me that people with similar income should receive similar payments.
But the disparities occurred even when racial groups had similar incomes and insurance coverage.
"We wanted to see if income tax systems treat people with similar incomes in the same way."
If individuals of similar income were grouped together, the outcome might be unstable.
The penalty mostly hits couples in which the two partners have similar incomes.
The writers were mostly poets and enjoyed a similar income.
That compared with only one of 17 black families who had similar incomes, adjusted for inflation, in 1967.
A private sector worker not in a defined benefit scheme (that's most of us) would need to have saved £675,000 to get a similar income.
But Americans generally have one thing in common with their neighbors: they have similar incomes.