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Exploring Iterative Enhancement for Improving Learnersourced Multiple-Choice Question Explanations with Large Language Models
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Proposes ILearner-LLM, which iteratively refines LLM-generated explanations for learnersourced MCQs using a fine-tuned generator and a fine-tuned evaluator that predicts student quality ratings and feeds scores back into generation.
Problem
Students often struggle to write high-quality explanations for the multiple-choice questions they author in learnersourcing platforms like PeerWise, and explanations are often omitted; automatic generation and evaluation of student-like explanations is needed, with limited high-quality training data
Approach
An explanation generator and an explanation evaluator (both instruction fine-tuned on PeerWise data) interact over K iterations: the predicted quality rating and the previous explanation are injected into the next generation prompt so the output is progressively improved toward student-like explanations.
Key results
- Fine-tuned LLaMA2-13B Merged with ILearner-LLM improved average BLEU on Auckland Law from 27.82 to 34.33 and Sydney Biology from 34.34 to 38.07.
- GPT-4 ILearner-LLM All History gave small gains over GPT-4 alone (e.g., Cardiff BLEU 29.08 to 30.43, UK Year 2 BLEU 30.67 to 31.83) with roughly 1.3-1.7 iterations needed to surpass the first output.
- Fine-tuned LLaMA2-13B Merged evaluator achieved MSE of 0.09-0.22 versus 3.02-3.95 for GPT-4 on most subjects (Auckland Law: 0.12 vs 0.42).
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Add iterative enhancement using the most recent explanation and rating to LLaMA2-13B Merged | LLaMA2-13B Merged · Five PeerWise subjects | BLEU: +5.33 | Helped |
| Add iterative enhancement using the most recent explanation and rating to GPT-4 | GPT-4 · Five PeerWise subjects | BLEU: +3.86 | Helped |
| Add iterative enhancement using all previous explanations and ratings (ablation) | GPT-4 ILearner-LLM · Five PeerWise subjects | BLEU: +0.82 BLEU and 0.05 improvement over GPT-4 on BERT score | Mixed |
| Use all previous explanations and ratings instead of only the most recent iteration (ablation) | GPT-4 ILearner-LLM · Five PeerWise subjects | BLEU | Mixed |
| Use all previous explanations and ratings instead of only the most recent iteration (ablation) | GPT-4 ILearner-LLM · Five PeerWise subjects | BERT Score | No clear effect |
Surprising findings
- Non-fine-tuned LLaMA2-13B and GPT-4 as evaluators tended to inflate scores, with MSE values around 3-4, which the authors attribute possibly to RLHF bias.
- Instruction fine-tuned LLaMA2-13B benefited more from iterative enhancement than GPT-4 did, the authors attribute this to alignment with the instruction format used during iteration.
Limitations
- GPT-4 evaluated on only 100 random test samples due to API cost, and the evaluator and generator reported on small test sets.
- Iterative gains for GPT-4 are small (e.g., BERT changes within about 0.05) and no significant difference between history variants was found.
- Evaluation relies on similarity to student-written explanations (BLEU/BERT) rather than human judgments of explanation quality.
Experimental setup
Datasets: PeerWise Sydney Biology PeerWise Cardiff Biology PeerWise Auckland Law PeerWise UK Medical Year 1 PeerWise UK Medical Year 2
Benchmarks: PeerWise five-subject MCQ explanation test sets
Metrics: BLEU BERT score MSE average quality rating score
Baselines: Vicuna-13B GPT-3.5 GPT-4 fine-tuned LLaMA2-13B LLaMA2-13B without fine-tuning
Builds on: instruction fine-tuning chain-of-thought prompting PeerWise
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