This group includes the various types of intellectual deficiency or feeblemindedness. The degree of mental deficiency should be determined by the history and the use of standard psychometric tests. The intellectual level may be denoted in the statistics by specifying moron, imbecile, idiot.

Acute, usually transient, psychoses of various forms occur in mentally deficient persons and commitment to a hospital for the insane may be necessary. The most common mental disturbances are episodes of excitement or irritability, depressions, paranoid trends, hallucinatory attacks, etc.

Mentally deficient persons may suffer from manic-depressive attacks or from dementia praecox. When this occurs the diagnostic grouping should be manic-depressive or dementia praecox as the case may be.

Mental deficiency cases without psychotic disturbances should go into the group of "Not Insane" under the appropriate sub-heading.