Real t-bill and bond yields have been falling for decades and are incredibly low right now, even negative (see chart below). With an eye to historical real returns of 2%, folks like Martin Feldstein think that bonds are currently mis-priced and warn that a bond bubble is ready to burst.
Investors need to be careful about comparing real interest rates over different time periods. Today's bond is a sleek electronic entry that trades at lightning speed. Your grandfather's bond was a clunky piece of paper transferred by foot. It's very possible that a modern bond doesn't need to provide investors with the same 2% real coupon that it provided in times past because it provides a compensating return in the form of a higher liquidity yield.
[By now, faithful readers of this blog will know that I'm just repeating the same argument I made about equity yields.]
Here's a way to think about a bond's liquidity yield. Bonds are not merely impassive stores-of-value, they also yield a stream of useful services that investors can "consume" over time. In finance, these consumption streams are referred to as an asset's convenience yield. (HT Mike Sproul)
For instance, the convenience yield of a house is made up of the shelter that the house owner can expect to consume. A Porsche's convenience yield amounts to travel services. What about a bond's convenience yield? I'd argue that a large part of a bond's convenience yield is comprised of the liquidity services that investors can expect to consume over the life time of the bond. Let's call this a monetary convenience yield.
In an uncertain world, it pays to hold a portfolio of goods and financial assets that can be reliably mobilized come some unforeseen event. A fire alarm, a cache of canned beans, and a bible all come to mind. Liquid financial instruments, say cash or marketable bonds, are also useful since they can be sold off quickly in order to procure more appropriate items. This ability to easily liquidate bonds and cash is a meaure of their monetary convenience.
Even if the unforeseen event for which someone has stockpiled canned beans or bonds never materializes, their holder nevertheless will enjoy the convenience of knowing that in all scenarios they will be secure. The stream of uncertainty-shielding services provided by both a bond and a can of beans are "consumed" by their holder as they pass through time.
This monetary convenience yield is an important part of pricing bonds. Prior to purchasing a bond, investors will appraise not only the real return the bond provides (the nominal interest rate minus expected inflation) but will also tally up the stream of future consumption claims that they expect the bond to provide, discounting these claims into the present. The more liquid a bond, the greater the stream of consumption claims it will yield, and the higher its monetary convenience yield. The greater the stream of consumption claims, the smaller the real-return the bond need provide to tempt an investor into buying. (HT once again to Mike Sproul on consumption claims)
Which brings us back to the initial hypothesis. If the liquidity of government debt has increased since the early 1980s, then we need to consider the possibility that bonds are providing an ever larger proportion of their return in the form of a monetary convenience yield, or streams of future consumption claims. If so, the observed fall in real rates isn't a bond bubble. Rather, negative real rates on treasuries may reflect technological advances in market microstructure and improvements in bond market governance that together facilitate the increased moneyness of bonds. Put differently, investors aren't buying bonds at negative real interest rates because they're stupid. It's possible that investors are willing to accept negative real interest rates because they are being sufficiently compensated by improving monetary convenience yields on bonds.
I find this story interesting because we usually think that in the long term, real interest rates are determined primarily by nonmonetary factors, including the expected return to capital investments and the time preferences of consumers. The story here is a bit different. In the long term, real interest rates on bonds are determined (in part) by monetary forces. The higher a bond's monetary convenience yield, the lower its real interest rate. Oddly, bonds may be bought not by consumers who are willing to delay gratification, but by impatient consumers who want to immediately begin consuming a bond's convenience yield (ie. using up future consumption claims). The line between consumption and saving is blurred and fuzzy.
In my previous post on equities, I gave some numbers as evidence for the increased liquidity of stocks. Bonds aren't my shtick, so I won't try to prove my hypothesis. All I'll say is that the rise of repo markets would have contributed dramatically to bond market liquidity since repo increases the ability to use immobilized bonds as transactions media. Give Scott Skyrm a read, for instance.
There is a case of missing markets here. If we could properly prices a bond's monetary convenience yield, then we could get a better understanding of the various components driving bond market prices over time.
Imagine a market that allowed bond investors to auction off their bond's monetary convenience yield while keeping the real interest component. Thus a bond investor could buy a bond in the market, sell (or lease) the entire chain of consumption claims related to a bond's liquidity, invest the proceeds, and be left holding an illiquid bond whose sole function is to pay real interest. By stripping out and pricing whatever portion of a bond's value is related to its monetary nature, investors might now precisely appraise the real price of a bond relative to its real interest payments. Excessively high real prices relative to real interest would indicate overvaluation and a bubble, the opposite would indicate undervaluation and a buying opportunity.
But until we have these sorts of markets, we simply can't say if bond prices are in a bubble. Sure, real rates could be unjustly low because bonds prices have been irrationally bid up. But they could also be justly low if bonds are simply providing alternative returns in the form of monetary convenience. Without a moneyness market, or a convenience yield market, we simply lack the requisite information to be sure.
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