For instance, the average pretax income of the top tenth of Americans has doubled since 1980, that of the top 1 percent has more than tripled, and that of the top 0.001 percent has risen more than sevenfold—even as the average pretax income of the bottom half of Americans has stayed almost precisely the same.

One key insight into these very high income households is they do best in bubble booms, like the 1920s where they controlled up to 45 percent of net worth, and the 1990s and 2000s, where they reached closer to 40 percent (although some studies found their assets reaching as high as 45 to 47 percent in recent peak years). (See Figure 1-18.)