- The denominator was not women or couples, the denominator was "households with children under 18". Thus any women without children or whose children are over 18 were not counted.
- 63% of the female breadwinner households were single mothers
- Of the 37% who were not single mothers, the only requirement was that they out-earn their husband. There is no mention of a minimum gap...so a wife who earns $1000/year more than her husband is counted the same way a wife earning $50,000/year more is counted.
Also interesting: married households with female breadwinners have an income of four times more than households with a single female at the head ($80,000/year vs $23,000/year). Households with a male breadwinner have a median income of about $78,000/year. This shows some interesting selection bias...my guess is that women who earn high salaries and out earn their husbands are less likely to quit/drop to part time when kids come on the scene. Since part of the normal debate around working/not working post-baby is "does my salary cover daycare costs", it would make sense that women who could answer a resounding "yes" would be more likely to stay on and keep the family income higher.