I'm not an expert on that. Maybe Michael Veall would like to comment on that.
Mobility is a very important issue, because again, even when you look at stable inequality, when you look at income distribution, we don't know it's the same people at the high end all the time. It may be people who are there once and then gone because they've had some large realization. So mobility is an important issue.
I can't give you too much detail, but maybe Michael....