Social mobility is a term of art that doesn't mean what people intuit it does. I think the question being asked here is "how easy is it to significantly increa

Social mobility is a term of art that doesn't mean what people intuit it does. I think the question being asked here is "how easy is it to significantly increase your income", which has an inverse correlation with social mobility. The reason for this is that high social mobility is most commonly an artifact of wage compression. Scandinavia has high wage compression, and the US very low wage compression, hence why it is much easier to significantly increase your income in the US than Scandinavia despite lower social mobility.