The Correlation Conundrum

A new study from the Bank of International Settlements (BIS) raises doubts about the value of commodities as a tool for enhancing portfolio diversification. The paper’s smoking gun, so to speak, is that “the correlation between commodity and equity returns has substantially increased after the onset of the recent financial crisis.” Some pundits interpret the study as a rationale for avoiding commodities entirely for asset allocation purposes. But that’s too extreme.

In fact, this BIS paper, although worth a careful read, isn’t telling us anything new. That said, it’s a useful reminder for what should have been obvious all along, namely: there are no silver bullets that will lead you, in one fell swoop, to the promised land of portfolio design. The idea that adding commodities (or any other asset class or trading strategy) to an existing portfolio will somehow transform it into a marvel of financial design is doomed to failure. Progress in the art/science of asset allocation arrives incrementally, if at all, once you move beyond the easy and obvious decision to hold a broad mix of the major asset classes.
Correlations are a key factor in the design and management of asset allocation, but they’re not the only factor. And even if we can find assets and strategies with reliably low/negative correlations with, say, equities, that alone isn’t enough, as I discussed last week. You also need to consider other factors, starting with expected return. It may be tempting to focus on one pair of assets and consider how the trailing correlation stacks up today. But that’s hardly the last word on making intelligent decisions on how to build a diversified portfolio.
Perhaps the first rule is to be realistic, which means recognizing that expected correlations, returns and volatility are in constant flux—and not necessarily in our favor, at least not all of the time. Bill Bernstein’s recent e-book (Skating Where the Puck Was: The Correlation Game in a Flat World), which I briefly reviewed a few months ago, warns that the increasing globalization of markets makes it ever more difficult to earn a risk premium at a given level of risk. As “new” asset classes and strategies become popular and accessible, the risk-return profile that looks so attractive on a trailing basis will likely become less so in the future, Bernstein explains. That’s old news, but it’s forever relevant.
As more investors pile into commodities, REITs, hedge funds, and other formerly obscure corners, the historical diversification benefits will likely fade. Granted, the outlook for expected diversification benefits fluctuates through time, and so what looks unattractive today may look considerably more compelling tomorrow (and vice versa). But as a general proposition, it’s reasonable to assume that correlations generally will inch closer to 1.0. That doesn’t mean that diversifying across asset classes is destined to become worthless, but the expected payoff is likely to dim with the passage of time.
The good news is that this future isn’t a total loss because holding a broad set of asset classes is only half the battle. Your investment results also rely heavily on how and when you rebalance the mix. Even in a world where correlations are higher and expected returns are lower, there’s going to be a lot of short-term variation on these fronts. In other words, price volatility will remain high, which opens the door (at least in theory) for earning a respectable risk premium.
Still, it’s wise to manage expectations along with assets. Consider how correlations have evolved. To be precise, consider how correlations of risk premia among asset classes compare on a rolling three-year basis over the last 10 years relative to the Global Market Index (GMI), an unmanaged market-weighted portfolio of all the major asset classes. As you can see in the chart below, correlations generally have increased. If you were only looking at this risk metric in isolation, in terms of history, you might ignore the asset classes that are near 1.0 readings, which is to say those with relatively high correlations vis-a-vis GMI. But by that reasoning, you’d ignore foreign stocks from a US-investor perspective, which is almost certainly a mistake as a strategic decision.

Nonetheless, diversifying into foreign equities looks less attractive today compared with, say, 2005. Maybe that inspires a lower allocation. Then again, if there’s a new round of volatility, the opportunity linked with diversifying into foreign markets may look stronger.
The expected advantages (and risk) with rebalancing, in other words, are constantly in flux. The lesson is that looking in the rear-view mirror at correlations, returns, volatility, etc., is only the beginning—not the end—of your analytical travels.
Sure, correlations generally are apt to be higher, which means that it’s going to be somewhat tougher to earn the same return at a comparable level of risk relative to the past. But that doesn’t mean we should abandon certain asset classes. It does mean that we’ll have to work harder to generate the same results.
That’s hardly a new development. In fact, it’s been true all along. As investing becomes increasingly competitive, and more asset classes and strategies become securitized, expected risk premia will likely slide. But what’s true across the sweep of time isn’t necessarily true in every shorter-run period. The combination of asset allocation and rebalancing is still a powerful mix—far more so than either one is by itself. And that’s not likely to change, even in a world of higher correlations.

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