A method for determining a causal relationship between events in a plurality of parameter time series, the method including: identifying a first event associated with a parameter excursion event; identifying a second event associated with a failure event, wherein there are a plurality of events including the first events and second events; determining values of transfer entropy for pairs of the events to establish a causal relationship for each of the pairs of events; using the determined values of transfer entropy and identified causal relationships to determine a process network, wherein each of the events is a node in the process network, the edges between nodes being dependent upon the values of transfer entropy; identifying a directed cycle within the plurality of events and the causal relationships; classifying a directed cycle; and classifying one or more events having a causal relation to the classified directed cycle.