How useful is international diversification?

I have a confession to make! In the ERN family portfolio, we have almost no international diversification. We invest the bulk of our financial portfolio in U.S. index funds; FUSVX and FSTVX, which are Fidelity’s (lower-cost) alternatives to the Vanguard Admiral shares VFIAX and VTSAX, respectively. Our international exposure is in the low single-digit percentages. How come, you ask? How useful is international diversification, anyway? Jack Bogle, for example, claims that with a diversified U.S. equity portfolio you will capture pretty much the entire global economy already because U.S. corporations do business all over the world. That argument, of course, is not very convincing. Doing business abroad obviously means that you get some diversification, but it definitely doesn’t imply you get enough diversification from a U.S.-only portfolio. To see how flawed that “revenue from all over the world” logic is, keep in mind that Apple is generating revenue from “all over the United States” but nobody in their right mind would ever call for investing exclusively in Apple stocks as a good proxy for the entire U.S. stock market.

Let’s look at the chart below to see how the U.S. stock market is clearly not a very precise proxy for international stocks. It’s a scatter plot of U.S. monthly equity returns on the x-axis and global returns (both non-U.S. and all global stocks). World ex USA has only a 0.65 correlation with U.S. equities. If for most x-values the blue dots are scattered around the 45-degree line +-/10% or even +/-15% (monthly!!!) then we clearly don’t capture everything going on in the world with a U.S.-only equity fund. (Of course, the overall World index has a much higher correlation; the orange dots are closer to the 45-degree line, but that’s mostly because global stocks already include the U.S. with a weight of about 50%.)

Diversification Chart01
Scatter Plot of U.S. equity returns (x-axis) and global equity returns (y-axis,). The correlation with non-U.S. stocks is only 0.65. All index data from MSCI.

So, diversification could theoretically work! Then why am I not more enthusiastic about international diversification? Very simple:

It’s less about whether diversification works. It’s more about when diversification works and especially when it doesn’t.

Let’s look at the data some more…

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Have bonds lost their diversification potential?

If you are a regular reader of this blog you’ll notice that we don’t like bonds very much:

Add to that our series on safe withdrawal rates where we found that over a long retirement horizon bonds become much less attractive. In the Trinity Study with retirement horizons of 15-30 years, you can get away with a bond share as high as 50%. But over long horizons of 40-60 years in the FIRE community, the low expected returns of bonds can jeopardize the sustainability of the portfolio as we showed in part 2 of our series.

Has anything changed since last year? Are we now a bit more optimistic about bonds? After all, yields have risen. The 10-Year Treasury yield reached 2.6% earlier this year but has since fallen again to about 2.2-2.3% just last week.

Let’s look at the numbers in more detail

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