Bloomberg: Using ETF flows to derive "sentiment" is difficult partly because many different types of investors use the products. Yet trading-oriented investors tend to flock to super-liquid ETFs such as SPY, IWM and QQQ. As result, rapid outflows from these ETFs are sometimes interpreted as retail investors capitulating, when the opposite is true. Retail investors -- led by advisers -- tend to put low cost above liquidity and thus allocate to products from Vanguard, Schwab and the iShares core series. To help clarify this distinction, BI created two indexes to track flows for each group, comprising ETFs focused on asset classes such as U.S. and foreign stocks, high-beta sectors and junk bonds. #stocktalk