A method of analysing the breathing of a subject 104, comprising: projecting a pattern of radiation onto at least part of a body of the subject 104； recording at each of a plurality of instances in time image data representing a three dimensional configuration of at least a portion of the projected pattern at that instance in time； processing the image data to produce a data array representing a shape of at least, part of the body of the subject 104 as a function of time； and calculating a value indicative of disorder for one or more values or parameters of or calculated from the data array. The value indicative of disorder may be an entropy value, and may comprise an approximate entropy value or a sample entropy value. Calculating the entropy value may comprise calculating an entropy value for a comparative parameter which may comprise a phase angle or a principle angle and/or spread. Respiratory rate, tidal volume, minute ventilation, peak inspiratory flow, fractional inspiratory time, peak and/or mean inspiratory and/or expiratory flow measures and the percentage contribution of the chest and/or abdomen to the tidal volume may also be calculated.
