REVIEW 5 major objections 3 minor 35 references
Clinical trial cohort selection using Large Language Models on n2c2 Challenges
T0 review · 5 major / 3 minor · reviewed 2026-08-10 · deepseek-v4-flash
Pith's one-line read Open-source LLMs fall short on nuanced patient-selection criteria
desk verdict A useful small-model benchmark on n2c2 cohort selection, overbroad in its 'generative LLMs underperform' conclusion; the empirical pattern is real but confined to the tested models and prompt family. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The argument is carried by a two-stage benchmark comparison. Stage one scores seven open-source LLMs on the 2018 cohort-selection task under three prompt recipes—a basic prompt, few-shot learning, and an iterated few-shot version whose examples are selected from earlier mistakes—each run with five-fold cross-validation and measured by per-criterion F1. Stage two takes the best-performing model from stage one and applies the same iterated few-shot procedure to the 2006 smoking and 2008 obesity tasks. The decisive comparison is between these generic-prompt LLM scores and the published best results from the original shared-task campaigns, especially the per-criterion breakdown on the 2018 task, which exposes exactly where the models fail.
What would settle it
Run the same three n2c2 tasks through a current larger open-weight model, or a commercial API on de-identified records that comply with the data agreement, using the same five-shot chain-of-thought prompts. If that model meets or beats the original challenge winners on the nuanced 2018 criteria—abdominal surgery, recent myocardial infarction, drug abuse, and decision-making capacity—while keeping the simple-criterion scores high, the paper's claim that generative LLMs do not generally outperform existing methods would be refuted for that model class.
Extended reading notes
Core claim
Using the three n2c2 challenge datasets as a controlled benchmark, the paper's central empirical claim is that open-source LLMs with generic prompting perform poorly as selection criteria become nuanced. On the 2018 cohort-selection test set, the best of the seven tested models post F1 scores ranging from below 0.1 to about 0.6 on nuanced criteria such as abdominal surgery, myocardial infarction within six months, drug abuse, and decision-making capacity, while the original challenge winners scored above 0.87 on those same criteria; on plainly worded criteria such as aspirin use the LLMs match or exceed the campaign baseline. The same split appears on the 2006 and 2008 tasks: smoking status and several co-morbidity labels are handled reasonably, while under-specified or judgment-heavy categories lose ground. The authors therefore conclude that their results run counter to the view that generative LLMs generally outperform existing methods or are likely to solve patient selection once and for all.
Load-bearing premise
The conclusions assume that seven open-source models prompted with one generic recipe stand in for 'LLMs' broadly; a newer, larger, or differently prompted model could still outperform the traditional systems on the nuanced criteria.
Editorial extensions
If this is right
- Simple eligibility criteria such as smoking status or aspirin use can be screened automatically with these models, reducing manual chart review for those parts of a protocol.
- Criteria requiring inference or judgment—abdominal surgery history, drug abuse, decision-making capacity—should be routed to human review or rule-based verification rather than accepted from an LLM.
- Choosing and iteratively curating few-shot examples is a measurable performance lever; the iterated few-shot prompt consistently beat the basic and plain few-shot prompts.
- Medical-domain pretraining did not automatically help: the general-text models outperformed the medical-specific model on the 2018 tasks.
- Claims that LLMs beat existing patient-selection systems need the same per-criterion benchmark comparison used here, because overall scores can hide failures on hard criteria.
Reading between the lines
- The paper's scope is deliberately limited to models that can run on an academic computing cluster, so its negative conclusion is a statement about that model generation and prompt recipe, not a law; the same protocol applied to newer or larger models could shift the balance on nuanced criteria.
- A practical deployment that follows from the results is a two-tier screen: let an LLM flag patients who clearly pass or fail simple criteria, and send only ambiguous and judgment-heavy cases to human reviewers, cutting manual workload without trusting LLMs on the hard criteria.
- The per-criterion F1 gaps on the 2018 task are a ready-made diagnostic for future model releases: any model that closes those gaps while keeping simple-criterion performance would be evidence of genuine reasoning gains rather than better pattern matching.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper evaluates seven open-weight LLMs on three n2c2 clinical cohort-selection benchmarks (2006 smoking status, 2008 obesity comorbidities, 2018 trial eligibility criteria) using basic, few-shot, and iterated few-shot prompting, with 5-fold cross-validation on the training data and comparison to official challenge winners. The main finding is that the best tested models (vicuna-13b and mistral-7b-instruct) achieve competitive or strong F1 on simple criteria (e.g., smoking class, aspirin use) but perform poorly on nuanced criteria such as MI-6MOS (0.414), ALCOHOL-ABUSE (0.375), and DRUG-ABUSE (0.222), and the paper concludes in Section 6.1 that generative LLMs do not generally outperform existing methods for patient selection.
Significance. If the claim is scoped to the tested models and prompting regime, the paper provides a useful, reproducible benchmark: it uses public datasets, reports per-criterion F1, compares to official campaign winners, and uses open-weight models that can be run locally. The per-task breakdown in Tables 2-6 is informative, and the negative result on fine-grained criteria is a valuable cautionary data point. However, the broad conclusion about 'generative LLMs' is not supported by the evidence, as only seven small open-weight models and one generic prompting family were tested, which the authors acknowledge in Section 6.2. With a scoped conclusion and a clarified evaluation protocol, the paper would be a solid empirical contribution.
major comments (5)
- [Section 6.1] The sentence 'our results run counter to a common view that generative LLMs generally outperform existing methods, or are even likely to solve the problem of patient selection once and for all' overreaches beyond the evidence. The evaluation covers seven open-weight models, the largest being vicuna-13b, with a single generic prompt family and no commercial or larger open models, as Section 6.2 concedes. The empirical pattern is real for these specific models, but the general claim requires invariance across model scale, instruction tuning, and prompting. Please restrict the conclusion to 'the small open-source LLMs and generic prompts evaluated here' or substantially broaden the evaluation.
- [Section 4.1 and Tables 2/3] The method text says 'the average and standard deviation of their F1 score across the five folds', while the table captions say 'median and standard deviation over 5 runs' and report a single value with a parenthesized value. With the skewed per-fold results visible for models like open-orca-mistral-7b (0.000 on several criteria), the median and mean can diverge substantially. Please state explicitly which statistic is reported, report both where the distribution is skewed, and describe how the standard deviation is computed for a median.
- [Tables 2-6 and Section 6.1] Within-model and between-model comparisons are made using means/medians and standard deviations without any significance test, bootstrap confidence intervals, or correction for multiple comparisons. The claim in Section 6.1 that vicuna-13b has 'more stability (lower standard deviation)' is not formally tested. Given that five runs per fold are reported, please add bootstrap confidence intervals or a paired significance test across folds, and state whether sampling temperature and random seeds were fixed or varied.
- [Section 4.2] The section is titled 'Fine-tuning' but describes iterative selection of few-shot examples, not gradient-based fine-tuning. No training hyperparameters, epochs, losses, or updated weights are mentioned. As written, the stage-2 results in Tables 4-6 could be mistaken for fine-tuned outputs. Please either retitle the section (e.g., 'Few-shot example selection for n2c2-2006/2008') or provide the actual fine-tuning setup.
- [Section 4.1 and 5-fold protocol] The relationship between the five-fold cross-validation, the train/validation split, and the reported results on the 'val set' (Table 2) and 'test set' (Table 3) is ambiguous. It is unclear whether the five folds are formed from the original training set, how many folds are used to select few-shot examples, and whether the reported scores are averaged over folds for a single validation/test split. Please specify the exact data flow: how the few-shot examples are selected from each fold, how the validation set is used for model selection, and how the official test set is evaluated.
minor comments (3)
- [Section 3.1] The word 'interannotor' should be 'inter-annotator'; similarly, 'critera' appears in Section 2 (first paragraph) and should be 'criteria'.
- [Table 3] The row 'best from campaign' for ASP-MI (0.770) is lower than several LLM scores (e.g., vicuna-7b 0.878, mistral-7b-instruct 0.875); this is worth a sentence in the discussion, as it qualifies the overall underperformance narrative.
- [Section 5] The text says results are reported for 'the n2c2-2006 and n2c2-2008 challenge test dataset for the vicuna-13b model', but Table 4 also reports mistral-7b-instruct; align the prose with the tables.
Circularity Check
No significant circularity: the study is an empirical benchmark evaluation whose claims are grounded in external n2c2 test-set comparisons, not in assumptions equivalent to its conclusions.
full rationale
The paper's central claim — that open-source LLMs with generic prompts perform poorly on nuanced eligibility criteria — is derived from measured F1 scores on held-out n2c2 test sets (Tables 3, 5, and 6) compared with official campaign results. No parameter is fitted to the target outcome and then renamed as a prediction; the 'best LLM' selection uses a validation split of n2c2-2018, and the reported test-set numbers are out-of-sample. The authors' own prior work appears only as literature context: [21] Zaghir et al. and [31] Naguib et al. are cited for prompt-engineering patterns and for the separate claim that masked language models outperform LLM prompting in few-shot clinical entity recognition. Neither citation is load-bearing for the cohort-selection conclusion, because the paper's own tables carry the argument. The limitations section explicitly concedes the scope (no commercial LLMs, no prompt optimization, no chain-of-thought), which makes the conclusion narrow but does not make it circular. There is no derivation chain in which an output equals an input by construction, and no uniqueness theorem or ansatz is imported from the authors' prior work. The evaluation is self-contained against external benchmarks, so the appropriate finding is no significant circularity.
Assumptions & free parameters
assumptions (3)
- domain assumption The n2c2 gold annotations are correct and consistent.
- domain assumption Reported 'best from campaign' scores are reliable and comparable.
- domain assumption Validation-based few-shot example selection does not leak test information.
Cite this review
Pith. "Pith review of Clinical trial cohort selection using Large Language Models on n2c2 Challenges." pith.science (2026). https://pith.science/paper/WFXVTUYQ
@misc{pith2026250111114,
author = {Pith},
title = {Pith review of: Clinical trial cohort selection using Large Language Models on n2c2 Challenges},
year = {2026},
howpublished = {\url{https://pith.science/paper/WFXVTUYQ}},
note = {Machine review of arXiv:2501.11114}
}
read the original abstract
Clinical trials are a critical process in the medical field for introducing new treatments and innovations. However, cohort selection for clinical trials is a time-consuming process that often requires manual review of patient text records for specific keywords. Though there have been studies on standardizing the information across the various platforms, Natural Language Processing (NLP) tools remain crucial for spotting eligibility criteria in textual reports. Recently, pre-trained large language models (LLMs) have gained popularity for various NLP tasks due to their ability to acquire a nuanced understanding of text. In this paper, we study the performance of large language models on clinical trial cohort selection and leverage the n2c2 challenges to benchmark their performance. Our results are promising with regard to the incorporation of LLMs for simple cohort selection tasks, but also highlight the difficulties encountered by these models as soon as fine-grained knowledge and reasoning are required.
Figures
Reference graph
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