This disclosure is directed to devices, systems, and techniques for determining an efficacy of a treatment program. For example, a medical device system includes a medical device including one or more sensors configured to generate a signal that indicates a parameter of a patient. Additionally, the medical device system includes processing circuitry configured to receive data indicative of a user selection of a reference time; determine a plurality of parameter values of the parameter based on a portion of the signal corresponding to a period of time including the reference time. Additionally, the processing circuitry is configured to identify, based on a first set of parameter values, a reference parameter value, calculate a parameter change value, and determine, based on the parameter change value, whether an improvement or a worsening of the patient has occurred responsive to a treatment administered beginning at the reference time.