Abusing IQ tests in death penalty cases?

This seems pretty strange to me that IQ tests done after the person is charged or convicted of a crime should be relied on. There is too much of a possibility of gaming the system. From the New York Times.

A 44-year-man whose lawyers claim he is mentally retarded is scheduled to be executed Thursday evening in Huntsville, Tex., unless the United States Supreme Court agrees to hear his case. . . .

Mr. Woods’s lawyers argue that his intelligence scores are low enough that he should be spared because of the Supreme Court ban in Atkins v. Virginia. But several courts have rejected that claim. . . .

His intelligence was tested twice in grade school, and he received scores of 80 and 78, but defense lawyers argued that those scores should be adjusted downward to account for the age of the tests. As an adult, he was tested just before his trial and scored 70. A second test done in prison in 2002 showed him with an I.Q. of 68. . . .

An IQ of 84 being declared as mentally retarded seems bizarre.

Some state courts in Mississippi, Alabama and Texas have held that inmates with scores as low as 66 are not impaired, while an inmate in California with a score of 84 was declared mentally retarded. . . .

I found this: "The standard deviation used in many tests, including the Weschsler IQ test, is 15." If that is accurate here, that implies that 66.6 percent of the population falls between an IQ of 85 and 115. That means that people just slightly outside the normal range are classified as mentally retarded. The notion that about 16 percent of the population is mentally retarded seems pretty high.



Blogger Phillip said...

The math may not work, but it does explain a lot of choices that people make, doesn't it?

12/03/2009 2:11 PM  
Blogger Antique Cop said...

"The notion that about 16 percent of the population is mentally retarded seems pretty high."
I don't know. What percentage of the population do politicians constitute?

12/03/2009 2:23 PM  
Blogger Raven Lunatic said...

I was under the impression that, as the population aproached infinity, the curve approached normal. Further, given how much a college educated person's standard day to day interactions skews their perceptions of what the mean is, I'd be willing to say that yes, a full 16% may be significantly below average, and that the mean is significantly lower than I would put it based on gut feelings.

And yes, the IQ test is a normalized test with a mean of 100 and SD of 15. They recalibrate it every few years because, apparently, humanity is becoming smarter.

Though, I would question whether a Z <= -1 is incapable of knowing right from wrong (as CA seems to hold), or that there are, and should be, consequences of ones actions. A Z <= -2 might be getting there, but as you say, testing someone when they know that scoring badly could help them is definitely suspect.

12/03/2009 4:27 PM  
Blogger Jim W said...

You may not be surprised to learn that the lower IQ cohorts in the population are drastically overrepresented in prisons.

The likelihood that someone will be stupid enough to think it is a good idea to kidnap, rape and strangle your girlfriend's children correlates very well with the likelihood that someone will be one or two standard deviations below normal.

If his "childlike simplemindedness" had lead him to normal juvenile mischief such as pulling a cat's tail or throwing food, he wouldn't be on death row. He's on death row for the very un-child-like things he did with his adult body and child-like mind.

12/03/2009 5:18 PM  

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