Thursday Quickies: Moms as breadwinners

I've seen a few headlines in the past few days about the study that showed that moms are breadwinners in 4 out of 10 households.  It's based on this Pew Research study, and I feel like there's a few nuances not made clear in the headline:

• 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.