A method for operating a vehicle system of a motor vehicle for determining at least one state variable which describes the state of the driver, in particular the attention and/or fatigue of the driver, wherein the state variable is determined by using a reference data set which describes a reference state, in particular a normal state of the driver, wherein the conditions of a condition group are verified during an entire drive of the motor vehicle, and wherein when all conditions are established a reference data set is recorded so long as all conditions are established and the reference data set is analyzed for calibrating and/or adjusting at least one operating parameter of the vehicle system.