The prevalence of mental subnormality.

The criteria of mental subnormality are complex, uncertain, and not self-consistent. Confusion arises because of errors of measurement, faulty standardization of tests and measurements, differences in growth patterns, environmental influences, and lack of agreement between the different criteria for diagnosis. Fluctuations in the threshold of community tolerance make the term "mental subnormality" only a relative one, useful mainly for administrative purposes. There is evidence to suggest that mild subnormality is not an irreversible condition.SURVEYS OF PREVALENCE HAVE BEEN OF THREE MAIN SORTS: psychometric, clinical, and follow-up. Some of the main findings from each of these are summarized. Since mild subnormality is to a large extent a culturally determined disability, it follows that cultural changes can do much to diminish its occurrence. In particular, better maternal and child health services, more adequate educational provision, social welfare, vocational guidance and training services, and a condition of full employment would together greatly reduce the prevalence of this, the commonest form of mental subnormality.