Investors, Don’t Depend on Stocks and Bonds To Hedge Each Other

There’s nothing more beautiful to a professional investor than a negative correlation between stocks and bonds. When stocks have a bad month, bonds have a good month, and vice versa. Since their zigs and zags offset each other, the value of the combined portfolio is less volatile. The customers are pleased. And that’s how it’s been for most of the last two decades.

But for almost a year now, Bloomberg market reporters have been detecting anxiety from the pros that the era of negative correlation may be over or ending, replaced by an era of positive correlation in which stock and bond prices move together, amplifying volatility instead of dampening it. “Bonds Have Never Been So Useless as a Hedge to Stocks Since 1999,” read the headline on one article this May.

Yet hope springs eternal. The headline on a July 7 article was, “Bonds Are Hinting They’ll Hedge Stocks Again as Growth Bets Ease.”

In the big picture and over long periods, it’s obvious and necessary that stock and bond returns are positively correlated. After all, they’re competing investments. Each generates a stream of income: dividends for (most) stocks, coupon payments for bonds. If stocks get very expensive, investors will shift money into bonds as a cheaper alternative until that rebalancing makes bonds more or less equally expensive. Likewise, when one of the two asset classes gets cheap it will tend to drag down the other.

When the pros talk about negative correlation they’re referring to shorter periods—say, a month or two–over which stocks and bonds can indeed move in different directions. Lately two giant money managers have produced explanations for why stocks and bonds move apart or together. They’re worth understanding even if your assets under management are in the thousands rather than billions or trillions.

Bridgewater Associates, the world’s biggest hedge fund, based in Westport, Conn., says that how stocks and bonds play with each other has to do with economic conditions and policy. “There will naturally be times when they’re negatively correlated and naturally be times when they’re positively correlated, and those come from the underlying environment itself,” senior portfolio strategist, Jeff Gardner says in an edited transcript of a recent in-house interview.

According to Gardner, inflation was the most important factor in the markets for decades—both when it rose in the 1960s and 1970s and when it fell in the 1980s and 1990s. Inflation affects stocks and bonds similarly, although it’s worse for bonds with their fixed payments than for stocks. That’s why correlation was positive during that long period.

For the past 20 years or so, inflation has been so low and steady that it’s been a non-factor in the markets. So investors have paid more attention to economic growth prospects. Strong growth is great for stocks but doesn’t do anything for bonds. That, says Gardner, is the main reason that stocks and bonds have moved in different directions.

PGIM Inc., the main asset management business of insurer Prudential Financial Inc., has $1.5 trillion under management. In a report issued in May, it puts numbers on the disappointment the pros feel when stocks and bonds start to move in sync. Let’s say a portfolio is 60% stocks and 40% bonds and has a stock-bond correlation of -0.3, which is about average for the last 20 years. Volatility is around 7%.

Now let’s say the correlation goes to zero—not positive yet, but not negative anymore, either. To keep volatility from rising, the portfolio manager would have to reduce the allocation to stocks to around 52%, which would lower the portfolio’s returns. If the stock-bond correlation reached a positive 0.3, then keeping volatility from rising would require reducing the stock allocation to only 40%, hitting returns even harder.

PGIM’s list of factors that affect correlations is longer than Bridgewater’s but consistent with it. The report by vice president Junying Shen and managing director Noah Weisberger says correlations between stocks and bonds tend to be negative when there’s sustainable fiscal policy, independent and rules-based monetary policy, and shifts up or down in the demand side of the economy (consumption).

The correlation is likely to be positive, they say, when there’s unsustainable fiscal policy, discretionary monetary policy, monetary-fiscal policy coordination, and shifts in the supply side of the economy (output). One last thought: It’s a good idea to spread your money between stocks and bonds even if they don’t hedge each other.

The capital asset pricing model developed by William Sharpe in the 1960s says everyone should have the same portfolio, consisting of every asset available, and adjust their risk by how much they borrow. True, not everyone agrees. John Rekenthaler, a vice president for research at Morningstar Inc., wrote a fun article in 2017 about the different strategies of Sharpe and fellow Nobel laureate Harry Markowitz.