Designing from the Inside: A Design Rationale and Process Record for a Culture-Calibrated Digital Biomarker System for Adult ADHD Diagnosis

Being unrecognised in a diagnostic system is an invisibility problem with real consequences. For neurodivergent people, across populations, presentations, and geographies, the failure of clinical infrastructure to receive them accurately produces real outcomes: delayed diagnosis, accumulated damage, the specific cost of a body that has been broadcasting a signal no instrument was built to receive. This document describes the design of an instrument built to receive it. No validated digital endpoint for adult ADHD exists in Europe. What exists is a diagnostic infrastructure calibrated to performance, to the clinical presentation of dysregulation in the room where assessment happens. The population most consistently missed is the most adapted. The signal is present. The measurement is absent. This is a design rationale and process record for a culture-calibrated digital biomarker system that integrates into the patient's existing behaviour and measures the signal the body is already producing. It documents the problem identification, the design philosophy, the self-testing methodology, and what the testing revealed that had not been anticipated. The full technical and software architecture is contained in the appendix. It was designed from the inside. By someone who was part of the population it was built for. That is the methodology.