A computer-implemented method of determining a cause of a trend in vital sign data of a subject comprises obtaining vital signs data of a subject, determining a trend in the vital sign data over time and determining a most likely cause of the trend in the vital sign data in dependence on one or more stored weights each associated with one or more possible causes. Each stored weight is indicative of a likelihood of the associated cause being responsible for the trend in the vital signs data. The one or more causes may include a medication event in which the subject has taken a specified medication, and/or includes a missed medication event. The vital sign data may be obtained from a wearable electronic device. The device may output an alert for example by sending a text message or email. A computer-implemented method of generating the stored weights based on vital sign data for a plurality of individuals is also disclosed.
