I think that depends on one's definition of disposable income. I think technically it's more or less what I was calling "net". But many people use it to mean "after I pay my mortgage, and my utilities, and my other thing". The further we go in that second direction the more it captures what I'm getting at.
As an example, if I have kids who need daycare and one country provides free daycare and another does not, then we need to account for the cost of daycare in our equation. And that may or may not fall under one's definition of disposable income.
The further you go in that direction, the more you have to include personal circumstances and values and the less useful it is for general comparison. Of course, the whole premise of looking at just average net income is a bit odd, so looking at expected quality of life makes more sense anyways.
100%. To use my daycare example, if someone didn't have kids, they're not realizing any value out of that.
So sure, there's an even more nebulous "value to society" concept, but since TFA is trying to get to dollars and cents I was trying to focus it on overall personal value. But even then one needs to not treat tax dollars equally.
As an example, if I have kids who need daycare and one country provides free daycare and another does not, then we need to account for the cost of daycare in our equation. And that may or may not fall under one's definition of disposable income.