I found that stat weird until I realized that it accounts for both my wife and me.  Per adult person in my house, we are still far above the 7500 (closer to 12000), but not as bad as the 24000 annual that I was thinking about.  If you look at as per person in the house, we are now at 6000 and I have actually brought the average down.

I also own a duplex where I can figure the amount the tenants pay pretty well.  Per adult, one side pays roughly 15000 per year and the other pays 9k.  Per person, the one side pays roughly 7500 per year and the other pays 6k.  

I am not sure how the stats were done for this study, but this should give you an idea of why the stats may not be wrong.