Funds with the lowest costs attracted most investment dollars in the 10-year period ended last year, in a possible reflection of investors focusing on costs at a time of diminished and more volatile market returns, according to a new Vanguard study.

Specifically, Vanguard found that low-cost equity mutual funds and ETFs together attracted 86 percent of net cash flow into that investment category, while low-cost bond funds attracted 78 percent of net cash flow. When broken out as a separate category, low-cost equity ETFs attracted 59 percent of net investor dollars.

The Valley Forge, Pa.-based company said its study may reflect a shift in investor focus now that the generous returns of the 1980s and the 1990s have been replaced by more or less flat returns over the past 10 years with a lot more volatility. Investors may therefore be looking at cost as one of the few factors they can control.

“Costs are also important to the retired investor, as high costs can substantially reduce one’s income stream and principal balance over time,” said Francis Kinniry Jr., CFA, a principal in the Vanguard Investment Strategy Group, in a press release.

For the purposes of the study, a fund was considered “low cost” if its fees and expense ratios placed it in the lowest quartile of all U.S. funds, as measured by data from Morningstar, the Chicago-based fund research firm.

Kinniry also pointed to the proliferation of low-cost mutual funds and ETFs over the past 10 years and the greater availability of cost information online as factors that led investors to prefer low-cost products.

Vanguard, now the third-largest ETF firm based on assets, was a pioneer of low-cost index mutual funds in the 1970s. It has built on that reputation since launching its first ETF, often offering lower-priced products than its competitors in the ETF space.