Market Sentiment Analysis: Measurement, Validation and Failure Modes

Connected evidence: Compare this analysis with AI and Market-Crash Risk: Indicators, Probabilities and Limits, AI and Human Market Research: Complementary Roles and Governance, Business Responsibility And Sustainability Report — standalone versus consolidated analysis and Litigation And Regulatory Action Disclosure — standalone versus consolidated analysis.

Define the question before the score

A sentiment score is meaningful only when its population, source set, time window and intended use are defined. News headlines, company filings and social posts represent different speakers and incentives. Combining them into one number without weights or provenance creates false precision. A useful specification states whether the indicator describes attention, tone, disagreement or a tested relationship with a later outcome.

Build a time-correct dataset

Each observation should carry the time it became available to the researcher, not merely the date mentioned in the text. Duplicated syndicated articles, revised releases and messages posted after market close need explicit handling. Economic context should come from authoritative series such as the Reserve Bank of India's Database on Indian Economy, with release timestamps preserved. These controls reduce look-ahead leakage.

Evaluation checklist

1. Freeze a labelled test set before selecting the final model.
2. Report class balance, precision, recall and calibration by source type.
3. Compare the signal with simple baselines over rolling time windows.
4. Include transaction costs before testing an investable interpretation.
5. Monitor vocabulary and source-distribution drift after release.

Interpret correlation carefully

Prices can influence the language people use just as language may coincide with price changes. A historical association is not proof of causation, and a statistically detectable result may still be too small or unstable to use. Results should be shown across different regimes and with uncertainty bands. A failed or inconclusive test is part of the evidence and should not be removed from the record.

Use boundary

Sentiment is best used as descriptive context or as one controlled feature in a broader research process. It should not be presented as a guaranteed timing mechanism. Investors should assess objectives, risk, liquidity and source quality rather than act on a model label alone.