Update README.md

README.md

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 ## Dataset Overview
 
-DocAttriBench is a dataset for training and evaluating answer grounding in Document Visual Question Answering. The dataset is constructed from existing document VQA and document understanding datasets. From these source datasets, we use Docling to extract document layout elements and their semantic types, and **MAPPET** to obtain the bounding box of the evidence region supporting the answer. As part of MAPPET, during dataset construction, Qwen2.5-VL-7B-Instruct is used for answer abstraction and as the MLLM underlying the attribution step.
+DocAttriBench is a dataset for training and evaluating answer grounding in Document Visual Question Answering. The dataset is constructed from existing document VQA and document understanding datasets. From these source datasets, we use Docling to extract document layout elements and their semantic types, and **MAPPET** to obtain the bounding box of the evidence region supporting the answer. During dataset construction, we used Qwen2.5-VL-7B-Instruct for answer abstraction and applied MAPPET for source attribution using the perplexity scores produced by this model.
 
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