Portfolio Theory forward testing

Portfolio Theory has during many decades been considered as the holy grail of investment despite the fact that very few empirical studies in the public domain have shown that portfolio theory outperforms a random equal weighted portfolio. We will in this paper empirically investigate how successful portfolio theory is when it comes to generating large positive returns with low return volatility. The dataset that is used consists of approximately 4000 US stocks. We find weak support that portfolio theory by itself would have generated any returns different than a random portfolio allocation. In general optimized historical cumulative returns are not the same as forward cumulative returns.