A method of identifying consumption of a utility by devices in a group of devices, wherein each device in the group of devices has a plurality of device-states and is arranged to consume the utility, the method comprising, for a given measurement period in a supply of the utility to the group of devices: obtaining a time-based vector of total levels of consumption of the utility by the group of devices during the given measurement period; for each of a plurality of group-states, wherein each group-state corresponds to each device in the group of devices being in a corresponding device-state, calculating a score representing a likelihood that the group of devices is in the group-state during the given measurement period, wherein said score is based on a likelihood of the obtained vector occurring based on a multivariate statistical model, corresponding to the group-state, of the total level of consumption of the utility by the group of devices during a measurement period in the supply of the utility to the group of devices when the group of devices is in the group-state; and identifying, based at least in part on the calculated scores, a most likely group-state for the group of devices; characterized in that the multivariate statistical model for a group-state is based on: a predetermined mean vector, μ, representing a mean of a group of vectors, each vector in the group of vectors being a time-based vector, corresponding to the obtained time-based vector, of total levels of consumption of the utility by the group of devices during a respective measurement period when the group of devices is in the group-state; and a predetermined covariance matrix, C, representing a covariance matrix for the group of vectors. obtaining a time-based vector of total levels of consumption of the utility by the group of devices during the given measurement period; for each of a plurality of group-states, wherein each group-state corresponds to each device in the group of devices being in a corresponding device-state, calculating a score representing a likelihood that the group of devices is in the group-state during the given measurement period, wherein said score is based on a likelihood of the obtained vector occurring based on a multivariate statistical model, corresponding to the group-state, of the total level of consumption of the utility by the group of devices during a measurement period in the supply of the utility to the group of devices when the group of devices is in the group-state; and identifying, based at least in part on the calculated scores, a most likely group-state for the group of devices; characterized in that the multivariate statistical model for a group-state is based on: a predetermined mean vector, μ, representing a mean of a group of vectors, each vector in the group of vectors being a time-based vector, corresponding to the obtained time-based vector, of total levels of consumption of the utility by the group of devices during a respective measurement period when the group of devices is in the group-state; and a predetermined covariance matrix, C, representing a covariance matrix for the group of vectors. a predetermined mean vector, μ, representing a mean of a group of vectors, each vector in the group of vectors being a time-based vector, corresponding to the obtained time-based vector, of total levels of consumption of the utility by the group of devices during a respective measurement period when the group of devices is in the group-state; and a predetermined covariance matrix, C, representing a covariance matrix for the group of vectors.