1. A method for identifying elements of a faulty system, that are likely to contain the faults of the system, based on a set of test vectors output from the system wherein each test vector contains a set of test values, the method comprising the steps of: comparing the output test vectors with an expected set of output test vectors to identify faulty test values, with any differences between the output test vectors and corresponding expected test vectors indicating a failure of the test and indicating that at least one element of the system is faulty; identifying a set of candidate faulty elements for each of the faulty test values; and identifying elements of the system that are likely to contain the faults of the system by performing a partial intersection on the sets of candidate faulty elements wherein only elements associated with at least a predetermined number of faulty test values are selected.