This is an important way to look at the data. By looking at individuals over time, it essentially quantifies social mobility. But then you have to take it a ste

This is an important way to look at the data. By looking at individuals over time, it essentially quantifies social mobility. But then you have to take it a step further. Does the difference in individuals' mobility over time change over time? In other words, has social mobility gotten better or worse? Only then are you comparing apples to apples in pessimism/optimism.