EviReport: From Reasoned Outlines to Evidence Tracked Long-Form Reports

Evidence-intensive analytical reports are expected to be fact-dense, quantitatively correct, and supported by figures. Yet one-shot longform generation with large language models (LLMs) frequently produces fluent but undersupported drafts: core facts are missed, numbers drift, and key visuals are absent, making the report hard to trust. We propose EVIRE-PORT, an evidence-tracked report-writing workflow that improves reliability by (i) organizing corpus evidence into compact, traceable units and retrieves query-relevant subgraphs into retrieval-ready packages (ii) leveraging a reasoning-focused LLM sketches a high-level plan for full coverage, then a chat-based LLM sharpens it into a detailed hierarchical outline with explicit scope and ordering (iii) rive generation with a facts-first iterative loop: extracting verifiable facts, composing strictly from those facts, then triggering gap-aware append queries to fill missing evidence To evaluate both correctness and completeness, we introduce EviReportBench, a benchmark instantiated on data-rich indicator reports that measures factual accuracy (claim verification), factual coverage (quiz-based evaluation), and visual evidence integration (image recall). Across 8 topics, experiments show that EVIREPORT consistently outperforms strong baselines in factual coverage (2.16×), factual accuracy (+8.9 points), and visual evidence integration (+34 points), approaching the quality of expert-written reports across multiple dimensions. Write a research report on the spatiotemporal variation of water transparency in large lakes and reservoirs worldwide.