The invention relates to the determination of the clinical state of a subject. A respective adaptive transform is applied to at least one measurement signal acquired from the subject, each adaptive transform being dependent on previously acquired history data, and a diagnostic index is formed, which is dependent on the transformed measurement signal(s) and serves as a measure of the clinical state of the subject. In order to reliably evaluate the clinical state of a subject on a fixed diagnostic scale during changes in the state of the subject, some or all of the previously acquired history data on which an adaptive transform is currently dependent is replaced with other previously acquired history data when a predetermined event is detected. The predetermined event is indicative of a change in the respective measurement signal, and the introduction of the said other previously acquired history data sets the transform ready for the change.