Two fundamental tenets of modern portfolio theory are the notion of diversification and that the only risk that matters is beta. Rather than holding one or a few stocks, investors instead should hold a large basket of stocks. According to the theory, diversification helps investors minimize risk as most of the company-specific risk evaporates in a well-diversified portfolio.

The notion of diversification, however, assumes that risk can be measured and we know how to measure it. Events over the last few years have cast doubt on how risk should be measured and have forced many believers in modern portfolio theory to reassess their models and risk metrics.

Value investors understand that risk cannot be accurately measured. That is why they developed the concept of margin of safety – not buying a stock unless it falls significantly (about 30 per cent) below its intrinsic value. This provides a mechanism for reducing risk which is totally distinct from diversification. In addition, value investors manage risk by carefully examining why they are buying and what they buying.

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A value investor's checklist looks something like this:

These rules and steps seem to be more important than diversification in controlling and managing risk. We have come full circle to the value-investing concept of risk, and it is the Great Recession and panic of the last few years that are responsible for this.

George Athanassakos is a professor of finance and holds the Ben Graham Chair in Value Investing at the Ivey Business School, Western University.