3. A method as in claim 2 wherein: a second of said analysis algorithms is arranged to generate and compare word-level n-gram frequency lists and to produce a comparison result; and said predetermined algorithm includes calculating a confidence value by multiplying the said measure of the homogeneity by the total number of words of the word frequency lists generated for obtaining said measure of homogeneity, and, if this confidence value is less than a predetermined threshold, setting to substantially zero the value of the weight corresponding to said second analysis algorithm.
6. A method as in claim 3, including the steps of: presenting to the user, for each of a plurality of candidate documents stored in the retained text store, the respective dissimilarity measures and respective links to said plurality of stored retrieved tests, receiving from the user an allocated relevance value R in respect of a presented dissimilarity measure, and modifying said weights by multiplying each weight (Wi) by a respective weight factor (1+ki), where ki is a function of the contribution that the respective weighted comparison result makes to the dissimilarity measure, and the value of R-Rmean, where Rmean is the mean of lowest and highest possible relevance values.