<![CDATA[Background. Digital interviews may offer scalable signals for identifying adolescents needing further assessment, but language models can appear accurate because of participant leakage, response length, or tuning-data evaluation. Objective. To develop and internally validate transcript-only probabilistic models of Patient Health Questionnaire-9 (PHQ-9) and Generalized Anxiety Disorder-7 (GAD-7) screening positivity in the Multi-Modal Psychological Assessment (MMPsy) corpus and quantify incremental performance beyond response length. Methods. This secondary prediction-modeling study used 1,275 participants with Mandarin transcripts and complete PHQ-9 and GAD-7 scores. Transcripts were represented by term frequency-inverse document frequency character 2–4-grams and modeled with elastic-net logistic regression. Five-fold outer cross-validation estimated performance in unseen participants; four-fold inner cross-validation selected penalization, fitted Platt calibration, and set fold-specific thresholds targeting 0.80 sensitivity. Comparators were response length and training-fold prevalence. Intervals used 2,000 participant bootstraps. Results. Screening positivity occurred in 258 (20.2%) PHQ-9 and 136 (10.7%) GAD-7 participants. Transcript areas under the receiver operating characteristic curve were 0.791 (95% confidence interval 0.761–0.820) for PHQ-9 and 0.822 (0.784–0.857) for GAD-7; precision-recall areas were 0.453 and 0.356. Calibration intercepts were 0.02 and −0.02; slopes were 1.10 for both. At sensitivity-directed thresholds, sensitivity was 81.4% and 80.1%, positive predictive value 36.1% and 23.5%. Improvements over response length were small and uncertain. Decision-curve patterns favored transcript content more consistently for GAD-7 than PHQ-9. Conclusion. Participant-wise transcript models identified screening positivity with useful internal ranking and high negative predictive values, but incremental value and clinical utility were outcome-dependent. External, prospective, subgroup, and workflow validation are required before operational use.]]>
