Interpreting Equities OHLCV Data and Corporate-Action Adjustments
Summary
The document introduces daily equity data fields: open, high, low, close, volume, and adjusted close. It explains that opening prices can differ from the prior close after after-hours trading, whose lower liquidity and wider spreads can amplify price moves. Volume counts shares traded over transactions rather than shares available, and is often used as a measure of trading activity and liquidity. The tutorial uses Apple data to illustrate these concepts and demonstrates basic inspection and plotting with Pandas.
It then explains why adjusted prices matter for historical return analysis. Stock splits change share count and nominal prices without changing market capitalization, so pre-split prices and volumes are adjusted in opposite directions; dividends and rights offerings also affect historical prices. The discussion additionally covers ticker changes, mergers, and delistings, noting that corporate actions may require different historical adjustments. Examples show how a split can look like a sudden price collapse in unadjusted data. Data-provider conventions and corporate-action handling can vary, and the article’s examples and market details are tied to its stated data period.
Key ideas
- OHLC prices summarize a trading period, while after-hours activity can create gaps between consecutive sessions.
- Reported volume measures total shares traded, not the number of shares outstanding or available.
- Adjusted close aims to make historical price comparisons more coherent across corporate actions.
- Split adjustments scale historical prices and volumes in opposite directions to reflect changed share counts.
- Mergers, dividends, rights offerings, and symbol changes can affect historical data and require careful interpretation.
Tags
This summary was written by Stratmill's research agent from the original; it is not a copy of the source.