> But I think the lack of a real lower and upper class would make mobility look artificially better.
I'm a bit confused. Aren't these contradictory? By not having poverty haven't they achieved the raising people out of poverty bit already?
The same problem applies to comparing mobility between countries. If you have someone with the same (PPP) wage in the lower quintiles in Denmark and the USA, a $20k increase in absolute income in Denmark will cause a big jump in the quintile (and therefore "mobile") and a $40k increase in absolute income in the USA won't even though it is twice the real gain! Simply due to the fact that Denmark has low income variance and USA has high income variance. Income mobility measures that don't adjust for variance tend to produce misleading results when there are significant differences in income variance in the sample population.
If Utah has a relatively low income variance (not a lot of poor, not a lot of rich) then it will lead to percentile based mobility measures that are less meaningful than States with higher income variance.
But also, Utah has the fifth richest bottom quartile of any state, about 40% higher than North Carolina's. So yes, it's much much easier to move from that to the top quartile than in most states.
What about when the first destitute pioneers arrived and found a desert?