A Novel Framework for Augmenting Rating Scale Tests with LLM-Scored Text Data

Psychological assessments are dominated by rating scales, which cannot capture the nuance in natural language. Efforts to supplement them with qualitative text have relied on labelled datasets or expert rubrics, limiting scalability. We introduce a framework that avoids this reliance: large language models (LLMs) score free-text responses with simple prompts to produce candidate LLM items, from which we retain those that yield the most test information when co-calibrated with a baseline scale. Using depression as a case study, we developed and tested the method in upper-secondary students (n=693) and a matched synthetic dataset (n=3,000). Results on held-out test sets showed that augmenting a 19-item scale with LLM items improved its precision, accuracy, and convergent validity. Further, the test information gain matched that of adding as many as 16 rating-scale items. This framework leverages the increasing availability of transcribed language to enhance psychometric measures, with applications in clinical health and beyond.