Between Multiple Choice and Open Response: Evaluating LLMs with Option-Free Deterministic Scoring

ZhongKen Hew, Sze Jue Yang, Chee Seng Chan


Abstract
Benchmark scores are treated as evidence of LLM competence, but the same knowledge can yield different scores under different question formats. MCQs provide objective and scalable scoring, but their answer options can turn recall into recognition through answer-option scaffolding. Open-ended constructed response questions (CRQs) remove answer options, but their scores often depend on human or LLM judges and rubric interpretation, introducing judge-dependent scoring. This creates a trade-off between removing answer-option scaffolding and retaining objective scoring. We study whether this trade-off can be reduced through Constrained Structured Response Questions (CSRQs), a structured-response protocol that removes final answer options while preserving deterministic scoring. CSRQs use multi-select, ordering, and matching outputs as auditable answer spaces for exact verification. We evaluate CSRQs using converted knowledge benchmarks and MyCulture, which is, to our knowledge, the first Malaysia-centred cultural benchmark in Bahasa Malaysia, with parallel MCQ, CSRQ, and CRQ formats. Across benchmarks and model families, scores change when the evaluation instrument changes, i.e., scores drop after answer options are removed, and CRQ scores vary across judges. These findings suggest that benchmark scores should be interpreted as products of both model capability and the test used to measure it.
Anthology ID:
2026.emnlp-main.844
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
19582–19605
Language:
URL:
https://aclanthology.org/2026.emnlp-main.844/
DOI:
Bibkey:
Cite (ACL):
ZhongKen Hew, Sze Jue Yang, and Chee Seng Chan. 2026. Between Multiple Choice and Open Response: Evaluating LLMs with Option-Free Deterministic Scoring. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 19582–19605, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Between Multiple Choice and Open Response: Evaluating LLMs with Option-Free Deterministic Scoring (Hew et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.844.pdf