Good catch; that axtually applies to both graphs. I will need to drag up some numbers on how many households have two income earners (as that is the only case where it would differ from the current setup). Of course, in absence of individual earner data broken out by age and income bracket (which I don't think is out there), any attempt to adjust will be just a guess.

Before I go out and try to find data, I'll say in advance the method and hypothesis: take the % of overall tax returns that involve two income owners. Increass the sample by that much: if 20% of 100 households have dual earners, that accounts for 120 total individual income earners. I predict that it will bring the national average down to be much more comparable with LW's stats.

(Forgive poor style, typing this from my phone)