I always am skeptical about these studies. For example Jeremy Siegel published a study on how the Dow Jones has performed between 1800 and today.
I once told Jeremy, “Look Jeremy, if you invested in 1800, in stocks in the U.S., 80% of the companies at that time were canal companies and banks. In the first big bust, the Depression of 1840, 1841, most of them went bankrupt. And eventually all the canal companies in America went bankrupt, all of them, even the most profitable ones, like Erie Canal.”
Then people invested in railroads in the 19th century. By 1895, 95% of the railroads went bankrupt. The studies don’t take these statistics into account; like how many companies failed if you had invested in stocks in 1929. Most of them no longer exist.