Patent ID: 8768718

Claim:
A method comprising: receiving, at an implantable medical device, patient data of a current patient; determining, at the implantable medical device, a reference group related to the current patient, the reference group including patients with at least one similar characteristic to the current patient; detecting, at the implantable medical device, a triggering event, the triggering event comprising an interrogation of the implantable medical device; updating, at the implantable medical device, the population of the reference group related to the patient in response to detecting the triggering event; determining, at the implantable medical device, a reference group dataset selected from the updated reference group, wherein the dataset includes patient data that is of a similar type received from the implantable medical device; generating, at the implantable medical device, a model of the reference group dataset, wherein the model is generated using a probability distribution function; and deriving a numerical index by calculating an area under the probability distribution function and using the area as the numerical index that indicates an activity index of the current patient, and wherein calculating the area under the probability distribution function comprises: identifying a plurality of points on the probability distribution function, the plurality of points having equivalent probability density and defining an interval or area of integration; and calculating the area of the interval or area of integration; and using the numerical index to determine at least one of: a similarity of the patient to the reference group, how likely the patient is to decompensate within a timeframe relative to a reference group's likelihood of heart failure decompensation in the timeframe, how likely the patient is to die in a timeframe relative to a reference group's likelihood of dying in the timeframe, how likely the patient's quality of life is to change a timeframe relative to a reference group's likelihood of quality of life changing in the timeframe, or stratify the patient into one or more discrete groups associated with one or more risk levels.