There are several anomalies in the stock market and they persist over time. Imitating Warren Buffett‘s stock picks is one of them. An academic study calculated that an ordinary investor could have outperformed the S&P 500 index by 10.75 percentage points EVERY YEAR between 1976 and 2006 simply by imitating Warren Buffett’s moves AFTER they are publicly disclosed. Isn’t this interesting? Here is the abstract of the study:
We analyze Berkshire Hathaway’s equity portfolio over the 1976 to 2006 period and explore potential explanations for its superior performance. Contrary to popular belief, we find Berkshire Hathaway invests primarily in large-cap growth rather than “value” stocks. Over the period the portfolio beat the benchmarks in 27 out of 31 years, on average exceeding the S&P 500 Index by 11.14%, the value-weighted index of all stocks by 10.92%, and a Fama and French characteristic-based portfolio by 8.56% per year. Although beating the market in all but four years can statistically happen due to chance, incorporating the magnitude by which the portfolio beats the market makes a luck explanation extremely unlikely even after taking into account ex-post selection bias. We find that Berkshire Hathaway’s portfolio is concentrated in relatively few stocks with the top five holdings averaging 73% of the portfolio value. While increased volatility is normally associated with higher concentration we show the volatility of the portfolio is driven by large positive returns and not downside risk. The market appears to under-react to the news of a Berkshire Hathaway stock investment since a hypothetical portfolio that mimics the investments at the beginning of the following month after they are publicly disclosed also earns significantly positive abnormal returns of 10.75% over the S&P 500 Index. Our evidence suggests the Berkshire Hathaway triumvirates of Warren Buffett, Charles Munger, and Lou Simpson posses’ investment skill unlikely to be explained by Efficient Market Theory.
However, we should note that Warren Buffett’s alpha disappeared over the last decade as Buffett shifted his focus to protecting his wealth instead of risking it.