A more direct example of the role of corpora in psycholinguistics can be seen from Garnham et al's (1981) study which used the London-Lund corpus to examine the occurence of speech errors in natural conversational English. Before the study was carried out nobody knew how frequent speech errors were in everyday language, because such an analysis required adequate amounts of natural conversation, while previous work on speech errors had been based on the gradual ad hoc accumulation of data from many different sources. However, the spoken corpus was able to provide exactly the kind of data that was required. Garnham's study was able to classify and count the frequencies of different error types and hence provide some estimate of the general frequency of these in relation to speakers' overall output.
A third role for corpora lies in the the analysis of language pathologies, where an accurate picture of abnormal data must be constructed before it is possible to hypothesise and test what may be wrong with the human language processing system. Although little work has been done with sampled corpora to date, it is important to stress their potential for these analyses. Studies of the language of linguistically impaired people, and of the language of children who are developing their (normal) linguistic skills, lack the quantified representative descriptions which are available. In the last decade, however, there has been a move towards the empirical analysis of machine-readable data in these areas. For example, the Polytechnic of Wales (POW) corpus is a corpus of children's language; a corpus of impaired and normal language development was been collected at Reading University, while the CHILDES database contains a large amount of impaired and normal child language in several languages.