A method of determining a fall risk of a user, the method comprising: collecting measurements of the motion of the user using a sensor; estimating a value for a parameter related to the gait of the user from the measurements using a processor; and determining a fall risk for the user, using the processor, from a comparison of the estimated value with a normal value for the parameter determined from motion of the user in which the user is at their normal risk of falling; characterized in that the step of estimating comprises identifying a step boundary in the collected measurements by: (i) identifying clusters of contiguous measurements in the collected measurements in which the magnitude of each of the measurements exceeds a threshold, apart from a gap in the measurements, wherein the magnitudes of the measurements in the gap are less than the threshold, provided that the gap covers a time period less than a time threshold; or (ii) identifying clusters of contiguous measurements in the collected measurements, wherein the first collected measurement in the collected measurements whose magnitude exceeds a first threshold denotes the first measurement in a cluster and wherein the first collected measurement after the first measurement in the cluster whose magnitude falls below a second threshold denotes the last measurement in the cluster, provided that the last measurement is more than a minimum period after the first measurement. collecting measurements of the motion of the user using a sensor; estimating a value for a parameter related to the gait of the user from the measurements using a processor; and determining a fall risk for the user, using the processor, from a comparison of the estimated value with a normal value for the parameter determined from motion of the user in which the user is at their normal risk of falling; characterized in that the step of estimating comprises identifying a step boundary in the collected measurements by: (i) identifying clusters of contiguous measurements in the collected measurements in which the magnitude of each of the measurements exceeds a threshold, apart from a gap in the measurements, wherein the magnitudes of the measurements in the gap are less than the threshold, provided that the gap covers a time period less than a time threshold; or (ii) identifying clusters of contiguous measurements in the collected measurements, wherein the first collected measurement in the collected measurements whose magnitude exceeds a first threshold denotes the first measurement in a cluster and wherein the first collected measurement after the first measurement in the cluster whose magnitude falls below a second threshold denotes the last measurement in the cluster, provided that the last measurement is more than a minimum period after the first measurement. (i) identifying clusters of contiguous measurements in the collected measurements in which the magnitude of each of the measurements exceeds a threshold, apart from a gap in the measurements, wherein the magnitudes of the measurements in the gap are less than the threshold, provided that the gap covers a time period less than a time threshold; or (ii) identifying clusters of contiguous measurements in the collected measurements, wherein the first collected measurement in the collected measurements whose magnitude exceeds a first threshold denotes the first measurement in a cluster and wherein the first collected measurement after the first measurement in the cluster whose magnitude falls below a second threshold denotes the last measurement in the cluster, provided that the last measurement is more than a minimum period after the first measurement.