A method for analysing sensor data in the form of parameters describing the condition of a subject the method comprising processing the sensor data to provide, at each of a plurality of time instants, a collection of two or more of the parameters, each of which parameters describes a different aspect of the subject's condition, the parameters together representing a state of the subject, putting together successive collections to form a sequence of states； and analysing the sequence to create a state machine representing the states of the subject detected over a period of time comprising the plurality of time instants.
