Monday, May 31, 2010

Court Decision: Thomas (Thomas v Allen, AL, 2010) affirmed as MR/ID

On May 27 the 11th Circuit Court of Appeals affirmed that Kenneth Thomas (2010) (click here for earlier 2009 decision) is a person with MR/ID and should be spared execution as per Atkins.  After a quick skim of the decision, it appears this, in my opinion, was the correct decision.  Thomas had numerous IQ scores below 70 during his developmental period and clear evidence had been presented regarding significant limitations in adaptive behavior during his developmental period.  This is a decision that appears to have been based on an objective evaluation of the facts and law and appropriate interpretation of SEM, and the AAIDD definition of MR/ID.

My only minor point of contention is that courts should not calculate the arithmetic mean of a number of IQ tests to get an average it is psychometrically flawed......calculating the average of standard scores requires formula that take into account the reliabilities of all tests, the SD's of all tests (if all the same this part of the calculations drops out), and the inter-correlations of all tests...before they can be mathematically averaged.  Since this is often not practical or realistic, when faced with multiple IQ scores over time, a more defensible approach would be to determine the median IQ value as the best estimate of the person's average IQ In this case it would not have made a difference..but, none-the-less, experts who provide advice to the courts should be familiar with this somewhat unknown no-no (i.e., averaging SS's).

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