The price, liquidity and information asymmetry changes associated with new S&P 500 additions
Why this work is in the frame
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Bibliographic record
Abstract
Purpose Using S&P 500 additions, the purpose of this paper is to test the permanence of abnormal returns around the index inclusion announcement and effective implementation dates to differentiate among competing explanations for the index inclusion premia puzzle. Design/methodology/approach The event study methodology is used to examine abnormal returns and volume effects around the announcement dates (ADs) and implementation dates of index additions. Findings This study documents a twofold increase in trading volume and significant permanent abnormal returns at the ADs that are correlated with subsequent decreases in bid‐ask spreads. There is a fivefold increase in trading volume, but only temporary abnormal returns, around the effective dates (EDs). Taken collectively, the evidence indicates that the permanent return at announcement is best explained by liquidity/information cost explanation, but the temporary return and large trading increases at the ED can best be attributed to the price pressure hypothesis. Research limitations/implications These results do not support the well documented long‐run downward‐sloping demand curve as the primary explanation for the abnormal returns observed on these dates. Originality/value This study contributes to the body of literature on the index inclusion effect by providing supporting evidence for the liquidity/information cost explanation, and by extending the previously analyzed index additions with an additional five‐year period from 2000‐2004.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it