The black line shows the total real return index of the US stock market and a demographic index. The demographic index attempts to examine the ratio of people reaching the peak age of producing more than they consume vs. those in the peak age of consuming more than they produce. The peak earning, producing, saving years tend to be at the age of the late 40s early 50s. The net consumers tend to be either retired or in the mid to late 20s taking on debt, thus consuming more than they produce.
Since the age structure of the country is known it is possible to project the relative number of people coming into a given age. When net producers are becoming more numerous the real return of the stock market tends to soar. When net consumers become more numerous the real return in stocks tends to stagnate or decline.