From the Census Bureau via Slate, on the income gaps between opposite-sex married couples:
- in 3.9 percent of couples, the husband earns 5,000 to 9,999 more dollars (per year) than the wife;
- in 25.4 percent of couples, the husband earns within 4,999 dollars of the wife;
- in 2.8 percent of couples, the wife earns 5,000 to 9,999 more dollars than the husband.
(The rest of the couples have more than a 10,000-dollar differential.)
Something seems fishy here. Call the wife’s earnings and the husband’s earnings ; we’re interested here in the distribution of the random variable . (Of course it’s difficult to write out the distribution of ; we know and are correlated, by assortative mating.) The three bins above correspond to being in the intervals and . The second interval is twice as wide as the others – so we’d expect twice as many couples to be in that middle bin as the ones on either side of it.
But instead we have six to nine times as many. Any explanations? All I can think of to explain this phenomenon – if it’s real – is that there are a surprisingly large number of cases where the husband and wife do the same job (not just working at the same place, but actually doing the same thing, for the same pay)… but how many couples like that can there be? It seems more likely to be an artifact of how the survey works.