The Night and Day of Amihud's (2002) Liquidity Measure

Amihud's (2002) stock (il)liquidity measure averages the daily ratio of absolute close-to-close return to dollar volume, including overnight returns, while trading volumes come from regular trading hours. Our modified measure addresses this mis-match by using open-to-close returns. It better explains cross-sections of returns, doubling estimated liquidity premia over 1964--2017. Using non-synchronous trading near close as an instrument reveals that overnight returns are primarily information-driven and orthogonal to price impacts of trading. Thus, including them in liquidity proxies magnifies measurement error, understating liquidity premia. Our modification especially matters when applications in finance and accounting render use of intraday data infeasible/undesirable.