In embodiments of the present invention periodic data is analysed by obtaining (SI) a vector of delay coordinates for each one of a plurality of samples of the periodic data in a time window and transforming (S2) each of the vectors into a coordinate system comprising a plurality of predefined vectors to obtain a projection of an attractor of the periodic data along one of the predefined vectors. The periodic data may be physiological data. Information representing one or more characteristics of the obtained attractor which is of diagnostic value is then displayed (S3) to enable a diagnosis.
