When measured using trade-time aggregation, intraday patterns in trading activity remain ∪ -shaped, but estimates of volatility and Kyle’s lambda fall sharply from open to close. ∪ -shaped patterns in volatility and Kyle’s lambda found using commonly-used calendar-time aggregation reflect over-aggregation biases when trading activity is high as near the open and close. Indicative of imperfectly-competitive liquidity provision, trade-time aggregation also reveals that in active markets, expected trade imbalances are positively priced and unexpected trade imbalances are more strongly priced when they share the sign of expected imbalances, while in less active markets expected trade imbalances are negatively priced. • When properly measured using trade-time aggregation, intraday patterns in trading activity are ∪ -shaped, but estimates of volatility and Kyle’s lambda fall sharply from open to close. • ∪ -shaped patterns in volatility and Kyle’s lambda found using commonly- used calendar-time aggregation reflect over-aggregation biases when trad- ing activity is high as near open and close. • Contrary to competitive liquidity provision, in active markets returns per- sist, expected trade imbalances are positively priced and unexpected trade imbalances are more strongly priced when they have the same sign as ex- pected imbalances. • In further contrast to competitive liquidity provision, in less active markets prices revert and expected trade imbalances are negatively priced.

We introduce a simple measure of informed trading risk, , the residual to liquidity quote‐improvement‐to‐deterioration ratio times . When facing with increased informed trading risk, liquidity providers compete less to provide liquidity, reducing their undercutting activity. Reductions in undercutting leave footprints in trade and quote data that are captured by . Unlike prior measures, is easy to construct, can be computed intraday, and is orthogonal to liquidity. The measure outperforms prominent existing alternatives in reflecting the extent of information asymmetry before earnings announcements, predicting unscheduled press releases, and identifying informed trading spillovers around them.

We identify Industry-Neutral Self-Financed Informed Trading (INSFIT) as stock trades financed by offsetting, equivalent dollar-denominated stock trades in the same industry. Approximately 37% of short-term mutual fund trading profits can be attributed to these trade pairs. Consistent with informed trading, INSFIT precedes unusually high media coverage for the underlying stocks. The trades underlying INSFIT are also larger as the release of stock-level news becomes more imminent. Both relative valuation and the hedging of industry exposure motivate INSFIT’s industry neutrality. While INSFIT positively impacts fund performance, active fund managers who execute INSFIT more aggressively obtain smaller trading profits per execution.

Tick sizes affect market quality through a tradeoff between pricing fidelity and undercutting. The U.S. Tick Size Pilot (TSP), which raised the minimum tick from 1¢ to 5¢, provides a natural experiment to study this tradeoff. We find that the TSP harmed liquidity for stocks with spreads below 10¢ but improved liquidity for stocks with spreads above 15¢. These opposing effects explain the mixed results across prior studies which pool together stocks with very different prevailing spreads. We recommend researchers using the TSP for causal inference should, at minimum, split samples at 10¢-spreads to account for these heterogeneous liquidity effects.

We study how intraday and overnight components of past returns predict future stock returns from 1926 to 2019. Portfolios formed on past intraday returns display momentum without long-term reversal, whereas portfolios formed on past overnight returns display no momentum. We link this asymmetric day-night pattern to the fact that most trading occurs intraday, which has remained stable over time. Evidence from international stock markets, intraday intervals, and analyst expectations suggests that investors underreact to private information revealed through trading. This underreaction mechanism is most consistent with Hong and Stein’s (1999) theory of momentum.

Order flow segmentation prevents direct interactions between U.S. retail and institutional investors. Using the imbalance in observable internalized retail trades, we show wholesalers use retail flow to provide liquidity to institutional investors, especially when liquidity is scarce. Our institutional liquidity cost ( $ ILC $ ) measures average absolute retail trade imbalances, positing that institutions holding stocks with greater such averages more often resort to the expensive wholesaler-provided liquidity. $ ILC $ is correlated with expected institutional price impacts. Unlike existing illiquidity measures, $ ILC $ has economically meaningful relations with institutional holding horizons and yields annualized liquidity premia of 2.7%–3.2% post-2010, even after excluding microcap stocks.