Originally posted by: Whisper
Originally posted by: PrinceofWands
You're asking some difficult questions, but I'll try to give you some basic answers. If you're really interested I can recommend a couple dozen good books to let you get a better handle on it.
IQ isn't really understood by many outside of academia. It gets tossed around and used incorrectly quite a bit. IQ, in its most correct usage, is a measure of 'g', which is a mental ability underlying all (or at least most) forms of cognition. There are a number of different tests available, each with certain benefits and hindrances. Outside of the Stanford-Binet (which is an entirely different type of test) the most important difference in tests is their 'g-loading', which relates to how much the test accounts for innate 'g' instead of acquired knowledge or specific areas of strength. In a highly 'g-loaded' test the distribution of scores across all tested areas will remain largely constant, indicating a single underlying factor. Good IQ tests have almost nothing to do with acquired knowledge.
Since you are in America I would assume you took the WISC as a child, though if you're old enough it might have been a Stanford-Binet. If you took the SB you have your answer, as it's an entirely different kind of test than others. The SB compares your actual knowledge with your chronological age against a baseline. It is a 16sd scale and is relatively un-g-loaded. If you took the WISC you still have your answer, because the testing for children is different than the testing for adults. This is to account for psychological/cognitive development which occurs in children at different ages, and is wholly different than the testing available for adults (the WAIS). It is completely common to see a 1sd disparity between WISC and WAIS scores.
It is more unusual for scores to increase when using the same test throughout one's adult lifetime, but it can still happen. In order to account for the Flynn effect tests are restandardized about every ten years. This can cause a disparity between the different test version results. Many kinds of brain injury or issues can alter ones performance on IQ tests. It is also possible to train one's 'g' within about 1sd (or in very rare cases 2sds) through careful targeting of specific skill areas.
If you want to be as sure as possible about your IQ I would recommend multiple tests every 10 years over 30 years. This should allow you to establish with confidence exactly where you are. I would recommend at least the WAIS, Cattell, Raven, and one of the larger non-verbals.
Actually, the current Stanford-Binet (SB5) has a standard deviation of 15, as it was changed largely in an attempt to become more uniform with other instruments that use standard scores with a mean of 100, such as the WAIS and WISC. As for g, the SB--just like the WAIS--taps into it, if you ascribe to the Spearman two-factor or Cattell-Horn-Carroll three-factor theory of intelligence. The SB and WAIS both produce very similar scores, although there are some differences between the two.
As for changes from WISC to WAIS, this usually isn't the case, as IQ tends to be fairly consistent across the lifespan after a certain age (from around 5-6 years onward, I believe). There technically shouldn't be much change moving from SB to WISC or SB to WAIS, either, as they all have fairly high correlations across all appropriate age group norms. However, when working in extremes (i.e., very high- or very low-ability individuals), you will likely see more fluctuation.
As for which tests to give/take, either the WAIS or SB5 would provide you an adequate picture of overall intellectual functioning. The use of a nonverbal IQ test above and beyond this might not provide much in the way of incremental validity, unless you suspected some type of language disorder or fluency issue, cultural interference, or something similar. There are likely other areas you'd want to assess over and above IQ that would be more appropriate, depending upon the nature of the testing.
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