The New York Times estimates that:
Now I'm certainly glad that defense lawyers will be able to raise the issue about this group, but the whole notion that this thing labeled I.Q. has any impact on the life of anyone seems quite absurd.
In fact, I find it hard to believe that anyone is still administering I.Q. tests for any purpose.
The only thing I.Q. tests measure is the facility of the person being tested at manipulating the sort of thing tested on I.Q. tests. This is no measure of whether someone should live or die -- or get a job -- or be accepted at a school -- or really, anything!
Anthropologist Scott Atran argues for retiring the whole idea of I.Q.
If your definition of what is "socially acceptable" is different from the test writer's you're dumb. Didn't you know that?
The late Stephen J. Gould pretty thoroughly demolished the concept of I.Q. in The Mismeasure of Man. I.Q. tests were devised by 19th and early 20th century researchers to give a "scientific" gloss to their favored racial and ethnic categories. The U.S. psychologist Henry H. Goddard tried his tests out on new immigrants (that is, southern and eastern Europeans) and concluded that
Robert Yerkes, a president of the American Psychological Association, got a chance to test the I.Q. of soldiers drafted for World War I and labelled "89% of negroes" as "feeble-minded." The content of his tests, which essentially measured familiarity with the mores and artifacts of upper middle class U.S. culture in his era, have been described acidly as a "kind of early 20th century Trivial Pursuit."
This "measure" measures only the assumptions of the measurer. The death penalty attracts and often depends upon this sort of insupportable pseudo-science. I.Q. and the death penalty are a toxic mix, despite the slight intervention from the court.