agreed. But that's a fundamentally different concept you are describing. The point is you cannot compare $100 salary and living in A with $100 salary and living in B unless you know the values of A and B. This definitely holds for "modern" western countries where social welfare/tax systems/costs of living/healthcare have a huge impact on living standards and hence what a salary of value X means. Generally speaking you might say more money == more fun, but I don't know of any data to back up that claim once we are talking about some dollar amount above the poverty limit.