Investors in U.S.-based funds added a net $15.4 billion to stock funds in the week ended Nov. 5, data from Thomson Reuters Lipper service showed on Thursday.

The money was poured overwhelmingly into exchange-traded funds, which reported net inflows of $15.086 billion. In contrast, stock mutual funds took in only $323 million of net new cash.

Funds invested through ETFs are commonly thought to represent institutional investors, with retail investors commonly thought to be mutual fund buyers. The ETF inflows were "mostly due to institutional investors hedging some of their short positions that they may have made," said Barry Fennell, a senior analyst with Lipper.

After the Bank of Japan on Oct. 31 surprised markets with more easing, investors around the world boosted equities. That left those with short positions likely scrambling, Fennell said, and other fast-moving institutional investors buying to capitalize on gains in the short-term.

Japanese equity funds also had significant inflows over the week: $777.5 million, their largest net inflows since March. All that new cash came from ETF investors, who poured another $779 million into the funds.

Retail investors, however, tend to behave very differently, Fennell noted. Those investors pulled a net $1.4 million from Japanese equity mutual funds.

U.S.-based taxable bond funds took in $6.3 billion in new money.

Corporate high-yield bond funds added a net $2.4 billion.

Money market funds took in $2.5 billion in net new cash.