An Intertemporal Study of ETF Liquidity and Underlying Factor Transition, 2009-2014

This article seeks to determine the migration of exchange-traded fund (ETF) liquidity and its factor constituents in the U.S. market over time, with the ultimate goal of making the ETF market more efficient and transparent. Using a set of factors commonly thought to impact liquidity, the authors develop a four-factor liquidity scoring algorithm (A-C liquidity score), extending the 2009 study by Agrrawal and Clark. The most liquid ETFs typically have lower bid–ask spreads, higher market capitalizations, lower expense ratios, and higher average trading volumes. The transition of ETF liquidity over the 2009–2014 period indicates that there is liquidity persistence and factor strengthening across all variables. Bid–ask spreads and expense ratios have compressed, which is a good trend for investors. Asset size and trading volume have gone up, which can be indicative of greater market participation and possibly high-frequency trading in the ETF environment. From 2009 to 2014, the ETF asset class has witnessed a phenomenal 34.9% annual growth rate, compared with a 19.8% growth rate in the Russell 3000 (the aggregate market capitalization for the ETF dataset increased from $438 billion in 2009 to$2,112 billion in 2014). The ETF ecosystem seems to be thriving as the new asset class of choice among both institutional and informed retail investors. However, there are two findings of concern. First, the overall beta of the ETFs in the study seems to have transitioned over time and moved up more than 9%. This may be due to increased cross-asset correlations, sector intertwining, global market cointegration, overlapping core constituents in ETFs, or simply a systematic upward drift in overall market risk premium; this limits portfolio diversification benefits. Second, over the five-year period, 25.7% of ETFs in the initial 622 ETF dataset (2009) were liquidated. This is an additional risk that investors and regulators have to keep in mind when evaluating ETFs. The cost of poor liquidity, overlooked by some retail investors, is often in the form of shallow market depth, high expense ratios, and a range of trade execution difficulties, besides potentially high tracking errors with the associated benchmark index. In conclusion, although ETF liquidity has grown significantly over time for most assets, there is some natural pruning, with pockets of concern. Overall, ETFs have rapidly become a viable and efficient instrument in the asset management landscape