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Can a Large Language Model Serve as the Missing Second Reviewer? Prominence Bias, Retrieval Effects, and a Confidence-Fabrication Gap in an Empirical Evaluation of Two Published Meta-Analyses

Fontelo P

2026

Abstract

Abstract Background Single-author systematic reviews (SRs) and meta-analyses (MAs) are common in the biomedical literature, yet methodological guidance discourages single authorship because a second independent reviewer reduces error and selection bias. Large language models (LLMs) have been proposed as a means of supplying that missing second reviewer, but existing validation studies are small (4–26 reviews) and largely single-condition. Objective To empirically evaluate two task designs — independent extraction from a known study list (“Design B”) and autonomous identification of studies from a research question alone (“Design A”) — and to characterize the specific ways an LLM second reviewer succeeds and fails. Methods A current-generation, publicly available LLM (Claude, Anthropic) was tested across repeated, independent sessions on two published meta-analyses selected for topical and temporal separation from one another: a metformin-and-cancer meta-analysis of 9 randomized controlled trials (RCTs) for Design B, and a multivessel-versus-culprit-only PCI meta-analysis of 9 RCTs for Design A. Design A was tested both without and with explicit retrieval-tool instructions. All model outputs were independently verified against primary sources by the author. Results In Design B (8 runs across two prompt-schema iterations), the model identified four real, independently verifiable errors in the published meta-analysis’s summary table, and separately produced one confirmed…

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