IMO, 3-6% moving all the way from bottom to top or top to bottom is actually quite good. I'd be extremely concerned if it was 20%, as that would imply the syst

IMO, 3-6% moving all the way from bottom to top or top to bottom is actually quite good. I'd be extremely concerned if it was 20%, as that would imply the system was nearly random. I'd also be concerned if it was 0%, as that would imply the system was static. 3-6% implies there is mobility, but it takes both hard work and luck to make it all the way from bottom to top. Likewise, half of families staying in either end quintile also seems healthy to me -- it implies half of families leave those quintiles, too. In an ideal world, what range would you like to see for those numbers?