The French person with a $44k/year salary has probably received free education, healthcare, childcare, pensions paid by employer, and other benefits over decades which together have more than made up the difference.

More importantly, disposable income is just income after tax and thus not a very useful reference: a difference in tax rates and services (e.g. cost of rent / mortage, healthcare, transportation, …) will skew this to very limited usefulness.

Either gross or discretionary income is a somewhat more useful point of comparison, disposable seems the least informative / most misleading comparison possible.

If it's disposable income, it doesn't matter if you put it in a pile and set it on fire, or choose to do home renovations. The fact that it's disposable means that it's left over after all of your necessities are taken care of.

No, the disposable income is just income after taxes. You're thinking discretionary income.

Which would probably a better point of comparison as disposable income is greatly skewed by how necessities are taken care of (aka how much is handled by the state — and thus through taxes — versus left to the individual).

The definition of disposable income here is merely income net of taxes.

Does it? I wonder if it accounts for how much more middle class Americans have to spend on their healthcare infrastructure than their french counterparts.