If you could select one of the following funds to serve as a diversifier for a stock-oriented portfolio, which would you choose?
I’m currently using Total Bond Market for the bond portion of my portfolio, but I’m considering switching.
The Differences
The difference in expenses between the funds is quite small, so that leaves two factors for deciding: credit rating and maturity.
The Total Bond Market fund is roughly 34% Treasury securities, 38% government-backed mortgage securities, and 28% corporate bonds. The other two funds are obviously 100% Treasury securities.
The Short-Term Treasury Fund has an average maturity of roughly 2 years, while the Intermediate-Term Treasury Fund and Total Bond Market fund have average maturities of roughly 6 years.
Treasury or Total Bond Market?
The primary reason I’m considering switching out of the Total Bond Market Index Fund is that it holds 28% of its portfolio in corporate bonds.
When investors get scared about the prospects of our economy (as they did in late 2008), they tend to sell corporate bonds as well as corporate stock. So it would seem reasonable to expect stock market performance to be more closely correlated to corporate bond performance than to Treasury bond performance. (The return data posted on Vanguard’s site seems to confirm that suspicion, though it only goes back to 1994.)
Their lower correlation to the stock market would mean that either of the Treasury funds would work as a better diversifier than the Total Bond Market fund.
The downside: Due to their lower-risk profiles, the Treasury funds should have lower expected returns than the Total Bond Market fund.
Short-Term or Intermediate?
The shorter a bond’s maturity, the less sensitive it is to inflation risk and interest rate risk. As a result, the short-term fund exhibits less volatility (in terms of annual returns) than the intermediate-term fund. In exchange, it should earn slightly lower returns over extended periods.
The flip side, however, is that precisely because of its greater exposure to interest rate risk, the intermediate-term fund has historically exhibited lower correlation to the U.S. stock market. (That is, during market crashes, if investors panic and flock to Treasury securities, interest rates will go down and bond prices will go up. The longer the maturity of a bond, the greater its price will increase.)
For me, if an asset class has higher long-term returns and lower correlation to the rest of my portfolio, that’s a good thing. And even if its stand-alone volatility is higher, it may lead to a less volatile overall portfolio.
What do you think?
As you can probably tell, I’m leaning toward switching to the Intermediate-Term Treasury Fund, but I’d love to hear your thoughts on the matter.
December 23, 2009 26 comments