1. A method of determining a reliability measure from a speech signal, comprising the steps of: deriving a word graph from the speech signal; deriving a concept graph with weighting values from said word graph; deriving a plurality sequences of attributes from the concept graph for a portion of data, with a weighting value being assigned to each sequence of attributes, wherein each attribute corresponds to a portion of the data; determining, from the weighting values of all sequences of attributes, probability values for said sequences; and generating a reliability measure for the portion of data using the sum of the probability values.