The most popular fund, in terms of net inflows, was the Vanguard 500 Index Fund, which took in $7 billion in January. The least popular, in terms of net outflows, was State Street’s SPDR S&P 500 ETF Trust, which lost $3 billion in assets.
Morningstar reports on net fund flows on a monthly basis, using an industry standard approach to measure the change in assets that is not attributable to the performance of the fund.