Do a few firms drive a century of stock market wealth?
Core argument: U.S. publicly traded stocks generated some $91 trillion in shareholder wealth enhancement over a 100-year period in the CRSP data, according to the author's calculations.
Two central conclusions emerge from this study of long-term investment outcomes in the CRSP data. First, stocks publicly traded in the U.S. markets were, despite periodic volatility, a tremendous source of wealth enhancement, totaling some $91 trillion by my calculations over the 100-year period. Second, long-term stock market outcomes demonstrate strong positive skewness, and the success of the overall markets is attributable to a substantial extent to very strong outcomes for a relatively few firms. This skewness is of practical importance. Financial planning is often based on expected or mean future returns. The outcome of such an exercise is informative, but it should be recognized that in a skewed distribution most possible future outcomes are less than the expected or mean outcome. While the distribution of possible outcomes to diversified portfolios is less skewed than for individual stocks, positive skewness is present at long time horizons in any case. Analyses focused on the median outcome, or better yet on the entire distribution of potential outcomes, are more informative. The historical U.S. stock return data shows that both buy-and-hold returns and dollar based measures of shareholder wealth enhancement are dominated by relatively few high performing firms.

