Presented are concepts for m classifying a disease or disability of a subject. One such concept comprises obtaining interaction data associated with a subject, the interaction data being representative of the subject's interaction with a movement-based input device. The interaction data is processed with a first machine learning process to determine a set of 5 characteristics for describing the subject. The set of characteristics is then processed with a second machine-learning process to generate a classification result for the subject. An instruction is provided to the subject for directing the subject to interact with the movement-based input device, wherein the instruction defines a challenge comprising a time-varying parameter.
