I thought it was that there is a spectrum for people who have ADHD as it’s neurological. I.e. you either have ADHD or not
You’ve perhaps conflated two opposing diagnostic approaches. The extant approach in most Western countries is to use the Diagnostic and Statistic Manual (DSM), which provides categorical guidelines for diagnosis of mental health disorders based on symptom clusters. Although not a contender or replacement for the DSM, a new approach that considers more factors has been developed by the US National Institute of Mental Health. This new approach is referred to as the Research Domain Criteria (RDoC) and it proposes basing diagnoses on both clinical observations AND objective neuroscientific methods. Part of the RDoC approach is to view disorders as reflecting multiple traits on a continuum (i.e. spectrum). It’s hoped this newer approach can improve care outcomes for disorders where symptom presentation varies greatly between individuals (i.e., schizophrenia) or genders (i.e., ASD).
