Apparatus and method for determining a likely cause or the likelihood of the occurrence of a cause of one or more effects, in which training data relating to previously identified relationships between one or more causes and one or more effects is used to learn the cause and effect relationship. A number of primary and secondary reference points are chosen in the input space created by belief values representing the strength of effect. A function representing the cause and effects relationship and a weight value is associated with each reference point. Weight values associated with primary reference points are considered as independent variables (primary weight values) and other weight values, which are associated with secondary reference points (secondary weight values), depend on one or more primary weight values. Belief value in the occurrence of likely causes of one or more given effects can be determined using this method or apparatus.