The principles of good experimental design will be illustrated by considering first what procedures are appropriate to provide phonemically-labelled data which is to be used for training and subsequently testing a recognition system . Aspects of these procedures and considerations will apply to a wide variety of experimental situations encountered in connection with language engineering. Finally, it ought to be noted that the performance of a recogniser (to be dealt with in Section 9.4) can only be as good as the data it is trained on, and that assessment results for recognisers will be misleading if the data used for training and testing are in error or if sampling biases are inadvertently introduced by adoption of inappropriate sample selection. Thus, there is a close relationship between the topics discussed here and those in Section 9.4.