An apparatus, and related method, for determining one or more association variables is described. The apparatus includes at least one processor, at least one memory, and at least one program module. The program module is stored in the memory and is configurable to be executed by the processor. The program module includes instructions for determining a statistical relationship between one or more temporal onsets corresponding to one or more events and a pattern of occurrence of a compound variable. The compound variable corresponds at least to a pattern of occurrence of a first variable and a pattern of occurrence of a second variable. The determining includes contributions from presence and absence information in the pattern of occurrence of the compound variable.