The present invention relates to a method and an apparatus for determining which one or more time series parameters of a plurality of time series parameters relating to operation of a system are correlated with a first operation state of the system. According to the invention, the method comprises providing time series data including data relating to a time series of each of the plurality of time series parameters; determining at least two first time periods, wherein the system is in the first operation state during the at least two first time periods; determining at least one second time period, wherein the system is in a second operation state during the at least one second time period; determining, for each respective time series parameter of the plurality of time series parameters, a first characteristic parameter relating to a first characteristic of the time series of the respective time series parameter for each of the at least two first time periods and the at least one second time period; and determining which one or more time series parameters of the plurality of time series parameters relating to the operation of the system are correlated with the first operation state of the system by determining, for each respective time series parameter of the plurality of time series parameters, whether or not the respective time series parameter is correlated with the first operation state of the system based on the first characteristic parameters of the respective time series parameter determined for each of the at least two first time periods and the at least one second time period.