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Fortunately, for the purposes of our discussion here, this matter can be fairly clearly put forth with the statement that the policy of adding to the field of mental retardation a wide area termed "borderline" is to be rejected. I strongly subscribe to that view and was pleased to find myself in agreement with an informal committee of experts the World Health Organization brought together in 1965. If you consult older psychological textbooks, you will find reference to the term "borderline intelligence". The AAMD's decision of 1959 to substitute for that term "borderline mental retardation" cannot be characterized as simply a semantic variation. It is unjustifiable for the reasons I have set forth earlier, and leads to endless confusion.

Where does this leave us as far as the boundaries of mental retardation is concerned? In former years, the likely answer in response to such a question would have been that an I.Q. rating of seventy to seventy-five on a Standard Intelligence Test would constitute the upper boundary and, indeed, I recall earlier years of institutional practice where this was a firm State policy. But today one would express this differently saying that, in general, the realm of mental retardation does not extend beyond an intelligence score of seventy to seventy-five but does, by no means, include all below such a score, and yet in exceptional cases may reach beyond it. In other words, what is suggested here is that it is no longer tenable to maintain a policy of designating all those with an intelligence rating below seventy to seventy-five as mentally retarded. Whether they should be so designated depends not just on measured intelligence but on the second criterion in our definition of mental retardation:

A distinct impairment of adaptive behavior of the social performance in day to day living normally expected from a person of a particular age by the community (or culture) of which he is a part.

Thus a man who scores an I.Q. of sixty-five on an intelligence test and who at the same time shows himself well able to adapt to the social demands of his particular evironment -sic- at home, at work and in the community, should not be considered retarded. And, indeed, we now know that he is not so considered and this, of course, is the reason why large scale attempts to identify the mentally retarded in a given community always ends up with a far smaller number of them than was predicted from the expected distribution of intelligence.

However, much as we are aware of this second criterion "social adaption", so far our attempt at quantifying it through measures similar to the various intelligence tests has failed. This then is the reason why we are unable, at this time, to give a clear answer to the question "Who are the mentally retarded and how many are there?"

One point seems to be clear -- the viewpoint which only a few years ago was almost universally accepted in this country and is still today expounded in textbooks and statements of public policy to the effect that three percent of the population is mentally retarded is no longer tenable.

But what do we know about the prevalence of mental retardation? We know that between one tenth and two tenths percent of the population, in other words one to two in a thousand, are so retarded as to require residential care under present circumstances. This is an area of wide international agreement as far as the so-called developed countries are concerned.

To a somewhat lesser extent there is agreement that in such countries between three and five tenths and four and five tenths persons per one thousand population would score an I.Q. below fifty.

In looking at these two figures in conjunction, it is important to realize that the first figure of one to two per thousand as needing residential care includes a substantial number of those who have a measured intelligence above an I.Q. of fifty but a marked impairment in social adaption.

Attempts to get a realistic estimate of how many mentally retarded there are beyond these two categories so far have resulted in widely varying figures -- the lowest ones coming from the Scandinavian countries. It is a sobering thought that we must today admit that we know far less than we thought we knew five to ten years ago!

But what about the qualitative aspect of mental retardation? What can be said about differential levels or degrees among the mentally retarded? Here, too, we are confronted with a realization that our knowledge is far less definitive than we had ever presumed. Twenty years ago, any student of psychology could quote, at the drop of a hat, that the mentally retarded were divided into morons, imbeciles and idiots and that these groups corresponded to I.Q.'s of from fifty to seventy (or seventy-five) in the first instance, from twenty-five to forty-nine in the second and from zero to twenty-four in the third. Somewhat later, increasing opposition was voiced to these particular terms and mild, moderate and severe were seen as more appropriate designations for these three levels and the WHO Report of 1954 (to which reference was made earlier) adopted these terms for its recommendation.