OP here. I am in the early chapters of John Bogle's "Little Book of Common Sense Investing," (which is great, btw). I flipped to his chapter on bond funds. It will probably not surprise many of you to hear that he's in favor of index funds for bonds, too.
Here are a few quotes:
"As a group, managers of bond funds will almost inevitably deliver a gross return that parallels the baseline... Yes, a few managers might do better ... by being extra smart, or extra lucky, or taking extra risk. Alas ... reversion to the mean often strikes. What's more, even if bond managers add a few fractions of a percent to the fund's gross returns, they rarely overcome the funds expenses, fees, and sales loads."
"Managers also may be tempted to increase returns by reducing the investment quality of their portfolio .... [which] subjects your bond investment to higher risk."
"Like stock funds, actively managed bond funds lag their benchmarks. Why? The arithmetic of costs."
"After their expense ratios, operating costs, and sales loads (if any) are deducted, their net returns will fall short [of the comparable indexes]."
[Citing a study] "During the 15 year period from 2001 to 2016, performance of the bond indexes is impressive, outpacing an average of 85% of all actively managed bond funds in the six categories -- short-term, intermediate-term, and long term grouped by US government and investment grade corporate sectors. The indexes also outperformed the managers of municipal bond funds (84%) and high-yield bond funds (96%). ... The average shortfall was about 0.55 percent per year."
"Once again, it is clear that low costs account for a dominant portion of the index advantage."
He quotes some others as well:
"Comparison of expenses, transaction costs, and where applicable, sales loads identify the cost advantage for bond index funds. For the actively managed load funds, the index fund advantage amounts to 1.2 percentage points per year ... [This] suggests how much additional return active management may have to add -- on average over an extended period -- just to break even!"
"You should not overlook the efficacy of index investing for bonds... The evidence is compelling and comes down firmly in favor of investing in index funds. ... This differential is largely due to fees."
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So, that settles the question for me. I trust Bogle's advice, along with what Audrey and others have shared. I'm going to forget about managed bond funds and stick with index funds. [There is the third option of trying to figure out how to invest in bonds myself, but I don't want to go that route -- too much trouble, and I'm not confident that I'll outperform an index.]
Thanks for the input, folks. You've been helpful as always.