The appearance of yet another rating scale for measuring symptoms of mental disorder may seem unnecessary, since there are so many already in existence and many of them have been extensively used. Unfortunately, it cannot be said that per-fection has been achieved, and indeed, there is considerable room for improvement.

Types of Rating Scale The value of this one, and its limitations, can best be considered against its background, so it is useful to consider the limitations of the various rating scales extant. They can be classified into four groups, the first of which hasbeen devised for use on normal subjects. Patients suffering from mental disorders score very highly on some of the variables and these high scores serve as a measure of their illness. Such scales can be very useful, but have two defects: many symptoms are not found in normal persons; and less obviously, but more important, there isa qualitative difference between symptoms of mental illness and normal variations of behaviour. The differencebetween the two is not a philosophical problembut a biological one. There is always a loss of function in illness, with impaired efficiency.