Individual and collective stock dynamics: intra-day seasonalities

TL;DR

This paper uncovers new intra-day patterns in stock behavior, showing how correlations, dispersion, and kurtosis evolve during trading hours, revealing the dominance of idiosyncratic effects early on and market influence later.

Contribution

It presents new stylized facts about intra-day stock dynamics, including correlation and kurtosis patterns, enhancing understanding of market behavior within trading days.

Findings

Correlation between stocks increases during the day

Kurtosis reaches a minimum at market open

Market influence grows as the day progresses

Abstract

We establish several new stylised facts concerning the intra-day seasonalities of stock dynamics. Beyond the well known U-shaped pattern of the volatility, we find that the average correlation between stocks increases throughout the day, leading to a smaller relative dispersion between stocks. Somewhat paradoxically, the kurtosis (a measure of volatility surprises) reaches a minimum at the open of the market, when the volatility is at its peak. We confirm that the dispersion kurtosis is a markedly decreasing function of the index return. This means that during large market swings, the idiosyncratic component of the stock dynamics becomes sub-dominant. In a nutshell, early hours of trading are dominated by idiosyncratic or sector specific effects with little surprises, whereas the influence of the market factor increases throughout the day, and surprises become more frequent.