On the whole, when psychiatrists get together in meetings or conferences, they have a fairly good idea of what they are talking about. Discussion flows in a more or less coherent way. Even if the topic involved is problematic—say, the diagnostic criteria for schizophrenia—there is a general sense of agreement about what is meant by the words ‘diagnosis' and 'schizophrenia’; even if the meanings are fuzzy at the edges. In areas of psychiatry made complex by the number of variables involved, statistical methods help to clarify the information gleaned, so that in the assessment of, for example, social factors in mental disorder, some clarity of conclusion prevails.