Message Level Polarity Eval

---
name: message-level-polarity-eval
description: Determines the overall sentiment polarity of an entire tweet, addressing class imbalance, slang, and informal social media text. Use when the user wants to benchmark on Twitter2015-test, or asks about evaluating this task. Reports macro-averaged F1.
metadata:
  skill_kind: dataset_eval
  source_arxiv: 1912.02387
  bibtex_key: rosenthal2015semeval
  confidence: high
---

# message-level-polarity-eval

> SemEval-2015 Task 10: Sentiment Analysis in Twitter — Rosenthal et al. (2015) (SemEval-2015 / arXiv:1912.02387, 2015)

## What this evaluates

Determines the overall sentiment polarity of an entire tweet, addressing class imbalance, slang, and informal social media text.

## Datasets

- **Twitter2015-test** — total ?; splits: test (-1)

## Metrics

- `macro-averaged F1` **(primary)** — range: [0, 1]
  - Harmonic mean of precision and recall averaged across all classes (positive, negative, neutral).

## Input / output format

**Input**: A full tweet.

**Output**: Sentiment polarity label (positive, negative, or neutral).

## Scoring recipe

```python
prec = rec = 0
for class in ['pos', 'neg', 'neu']:
    prec += precision(y_true, y_pred, class)
    rec += recall(y_true, y_pred, class)
macro_prec = prec / 3
macro_rec = rec / 3
f1 = 2 * (macro_prec * macro_rec) / (macro_prec + macro_rec)
```

## Common pitfalls

- Baseline majority class F1 is ~30.3%, so models must significantly outperform simple majority voting.
- Sarcastic tweets are a subset of the test set and evaluated separately; models trained on non-sarcastic data often degrade on this subset.

## Evidence (verbatim from paper)

> The results for subtask B are shown in Table 11. ... with an F1 of 64.84, unitn with 64.59, lislif with 64.27, and INESC-ID with 64.17.

## Citation

```bibtex
@misc{rosenthal2015semeval,
  title={SemEval-2015 Task 10: Sentiment Analysis in Twitter},
  author={Rosenthal et al. (2015)},
  year={2015},
  note={SemEval-2015 / arXiv:1912.02387}
}
```

- arXiv: 1912.02387