I think it's probably a proxy for talking about "discretionary income" or something. My kid may have more discretionary income than I do if he doesn't have to

I think it's probably a proxy for talking about "discretionary income" or something. My kid may have more discretionary income than I do if he doesn't have to pay a mortgage and utility bill every month. So a higher cost may actually be more affordable if other things don't have to be paid for. I don't really know how to compare countries like that- but I would wager somebody has tried.