It was my understanding that the frequencies did not follow the bell curve at the high end beyond a certain point for the IQ tests commonly used in the U.S. For example, a ton more kids tested at the 150+ Full Scale IQ on the WISC than bell curve statistics would have predicted. I heard that there are other ways to tease out a reliable estimate and I was simply wondering what was used.
You are correct. The data available at the high end of the curve is very sparse. This makes it difficult to tease out accurate normalized IQ scores.
To see one way this is done, I recommend reading the following official report on the WISC IV extended norms and how they were derived:
http://images.pearsonclinical.com/images/assets/WISC-IV/WISCIV_TechReport_7.pdfThe standardized IQ tests in common use for gifted children were developed to be accurate in the center of the bell curve, so they could identify abnormal IQ. They weren't designed to differentiate those in the highly gifted population in any way, although they are frequently used for this purpose.
