Intraday volatility

A Work Project, presented as part of the requirements for the Award of a Masters Degree in Finance from the NOVA – School of Business and Economics

Daily stock price volatility is found to be significanlty and frequently different whether measured via successive open or close prices. This induced different authors to the analysis of the volatility behaviour during the trading session in several important Stock Exchanges around the globe. This paper focuses on the analysis of the Portuguese case. The major finding is that intraday volatility tends to depict a U-shaped curve for the average variance of returns measured during the trading session. This has important implications for regulators and practioners since it suggests that prices discovered both at the opening and at the closing periods may not clearly reflect the market dynamics around these two moments. Few reasons are predicted for such misrepresentation. This analysis covers the main share index - PSI 20 - and three individual shares selected from different industrial sectors and with different levels of liquidity.