Research has shown that small cap, value, and high profitability stocks have higher expected returns than the market. They also exhibit imperfect correlation with the market. Building a portfolio that tracks the market, and then increasing the portfolio weight of small cap, value, and high profitability stocks increases the expected return and diversification of that portfolio. From a human investor’s perspective, the problem with higher expected returns is that they are expected, not guaranteed. And that imperfect correlation? It looks great on paper, but it means that when the market is up, the portfolio might not be up as much, or it might even be down. Performance that is different from a market cap weighted index is called tracking error. For the investor comparing their performance to a market cap weighted benchmark, negative tracking error can be unnerving, especially when it persists for long periods of time.
But tracking error is not risk. Risk is the probability of not achieving a financial goal. Diversification is well-established as a means to reduce risk, but it does not result in higher returns at all times. When a globally diversified portfolio underperforms the US market, it is not a reason to forget about International stocks. When stocks underperform bonds, as they did in the US between 2000 and 2009, we do not abandon stocks. Dismissing small cap and value stocks after a period of underperformance relative to the market is no different. They are factors that increase portfolio diversification and expected returns, leading to a statistically more reliable investment outcome. This remains true through periods of underperformance.
The real risk is investor behaviour. Think about enduring portfolio underperformance relative to the market for ten years or longer due to a small cap tilt. You made a conscious decision to tilt the portfolio based on the academic evidence, but there are no guarantees of outperformance. If an investor chooses to abandon their tilted portfolio after a period of underperformance, it is akin to selling low. If they subsequently invest in a market cap weighted portfolio, they are selling low and buying high. That increases the probability of not achieving a financial goal. That is risk.
We do not know how different asset classes will perform in the future. You may always wish that you were overweight US stocks before the US outperformed or underweight small caps before small caps underperformed. Hindsight is pretty good. Looking forward, all we can reasonably base objective investment decisions on is the academic evidence. The evidence indicates that, over the long-term, stocks can be expected to outperform bonds, small stocks can be expected to outperform large stocks, value stocks can be expected to outperform growth stocks, and more profitable stocks can be expected to outperform less profitable stocks. Tilting a portfolio toward these factors is expected to achieve better long-term results, but it will almost definitely result in tracking error relative to the market.
Bad investor behaviour due to tracking error is a real risk that needs to be managed in portfolio construction. If it can be managed, the door is opened to a statistically more reliable long-term investment outcome.