When I wrote the blog I had pulled that statistic from memory, and I have not been able to find a confirming source. The DSM itself says: “In approximately 30-40% of individuals seen in clinical settings, no clear etiology for the mental retardation can be determined despite extensive evaluation efforts.” (DSM-IV-TR, p 45)

Most authorities, however, quote higher figures. Ullmann and Krasner (A Psychological Approach to Abnormal Behavior, 1975) state: “The majority of retardates, approximately 75%, do not reveal any known physiological syndrome.” Valdosta State University, Georgia, under Causes of Mental Retardation, states: “cultural-familial retardation: about 75%.” (Cultural-familial is a residual category for cases where no physical etiology has been identified.) Biasini et al (Mental Retardation: A symptom and syndrome) state that in severe retardation “…30 to 40% of cases, the cause is reported to be unknown” while in mild retardation “between 45 and 63% of the cases are attributed to unknown etiology. (The area has been extensively studied, and you can find lots of similar references in the literature.)

So I don’t know where I got 50% – perhaps I had just combined these various numbers in a kind of senile blur.

My essential point is that a large proportion (approximately half) of the individuals who carry this diagnosis have nothing medically wrong with them. Or to be more precise: nothing that has caused their low intelligence. Their diagnosis of mental retardation is a result of the artifactual way that the diagnosis is assigned. What the DSM does is shoehorn these individuals into a medical category even though their problems are not medical. The diagnosis of mental retardation communicates a sense of hopelessness and helplessness which is unwarranted.

It’s a particularly complex and thorny area, because a diagnosis of mental retardation is considered a disability and qualifies an individual for a social security income, and I’m certainly not advocating anything that would result in increased hardship for these people. At the present time the only kind of disability recognized by the US Social Security Administration is medical disability. I would like to see this definition expanded to include areas such as low intelligence, so that these individuals could receive services and financial assistance without the pretense that they have a medical problem.

I think that the term mental retardation should simply be eliminated. The individuals who have a medical/physical etiology should be identified as such (e.g. microcephaly with severe functional limitations). And people with no physical problem/etiology should receive services and assistance under a different category.

Developing the theme further, I think the notion of identifying different kinds of disability is an important one. Habitual criminals, for instance, could be considered to be disabled in the sense that they don’t seem to have the same intuitive respect for the rights and comforts of others that the rest of us take for granted. Traditionally we conceptualize these individuals as simply “bad” and put them in prison (where they usually become “badder”). If we could promote the notion that these individuals were lacking something that most of us learn in childhood, then we might have more success with this population. DSM, of course, conceptualizes them as having a mental illness (conduct disorder, intermittent explosive disorder, antisocial personality disorder, etc.), but their problems are clearly not medical in nature and the medical model has had little success with these kinds of problems.

Anyway, as always, one thing leads to another. Thanks for your comment.