4 ms·

I thought: E[IQ] = 100, SD[IQ] = 10 then SD (for n = 37) = (10 / sqrt(36)) =~ 2 So a 10 point deviation between groups is 5 sd's, p <.001 ?

tokenadult 12y ago
The standard deviation of IQ scores is 15 by definition. (That is, raw scores on the item content of IQ test batteries are generally not reported at all, but rather what is reported for each test-taker is a standard score defined as performance at the norming population median level being an IQ of 100, and performance one standard deviation up from that being an IQ of 115, and so on. All mainstream individual IQ tests have been scored this way for just about all of my lifetime.) P.S. I would take four standard deviations up or down (the IQ range of 40 to 160) as the outer limit of validated IQ scores, and indeed few modern IQ test batteries purport to report scores outside this range. See https://en.wikipedia.org/wiki/IQ_classification https://en.wikipedia.org/wiki/IQ_classification and the published reference books cited there for more background. P.P.S. I should have mentioned when I first posted this comment that any IQ test has a standard error of measurement even if it is faultlessly administered and scored. Sometimes small-n studies like the study reported here have IQ score differences between two groups that are simply the result of the test errors showing a difference where no actual difference exists. IQ tests are often also very frequently administered incorrectly or scored incorrectly even if correctly administered, magnifying the size of the error band around the obtained score. For this study, I'm not sure if the human subjects tested were tested by test-givers who were "blind" to what group the test-takers were in, which could also be an issue.
- innguest 12y ago
  > All mainstream individual IQ tests have been scored this way for just about all of my lifetime. Correct me if I'm wrong but I thought the Cattell tests were obviously scored in the Cattell scale (24 s.d.) and the Stanford-Binet tests in the Binet scale (16 s.d.). When I was into reading about psychometrics it seemed to me that the cut off percentile was a more straightforward way to talk about IQ than using either of those three scales (Wechsler, Binet, Cattell).
  - tokenadult 12y ago
    The current Stanford-Binet test (and the next one, which is in preparation) use the typical 15 points per standard deviation scoring. The Cattell test is not a "mainstream" IQ test and correlates rather poorly with expected variables that ought to correlate well with IQ like academic achievement. Standard scores by the current definition are readily converted to percentile ranks by look-up tables, by the definition of standard deviation assuming a roughly normal distribution. As above, it's important to note that there is error in any IQ test. I've now had a chance to read the underlying papers related to this thread (which go back at least to 2008), and the IQ tests used in this study are even less mainstream than I feared. "A total of 240 individuals were evaluated with the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and the Wisconsin Card Sorting Test (WCST)." doi:10.1016/j.bbi.2008.04.156
TrainedMonkey 12y ago
That is true, but we can't translate 10% longer time taken on performing some task into 10% less effective IQ.
- duaneb 12y ago
  No, but there aren't really any good parameters for IQ, and time taken is a damn good, reliable, objective measure.
  - TrainedMonkey 12y ago
    Yes, but without knowing standard deviations and mean time taken for both groups we can't do math and claim any likelihood of observed result occurring in a random distribution.
leeber 12y ago
Guys, we're programmers here not statisticians: def test(): ... n1 = numpy.average(numpy.random.normal(100,15,52)) ... n2 = numpy.average(numpy.random.normal(100,15,40)) ... return abs(n1-n2) / ((n1+n2)/2.0) ... >>> vals = [test() for i in xrange(0,1000)] >>> numOver10 = len([v for v in vals if v > .1]) >>> numOver10 2
- tomrod 12y ago
  Crucial in your code is the standard deviation of 15. Where is that coming from? Ah, I see. Standard IQ normalizations.
  - leeber 12y ago
    http://en.wikipedia.org/wiki/Intelligence_quotient http://en.wikipedia.org/wiki/Intelligence_quotient

tokenadult 12y ago

The standard deviation of IQ scores is 15 by definition. (That is, raw scores on the item content of IQ test batteries are generally not reported at all, but rather what is reported for each test-taker is a standard score defined as performance at the norming population median level being an IQ of 100, and performance one standard deviation up from that being an IQ of 115, and so on. All mainstream individual IQ tests have been scored this way for just about all of my lifetime.) P.S. I would take four standard deviations up or down (the IQ range of 40 to 160) as the outer limit of validated IQ scores, and indeed few modern IQ test batteries purport to report scores outside this range. See https://en.wikipedia.org/wiki/IQ_classification https://en.wikipedia.org/wiki/IQ_classification and the published reference books cited there for more background. P.P.S. I should have mentioned when I first posted this comment that any IQ test has a standard error of measurement even if it is faultlessly administered and scored. Sometimes small-n studies like the study reported here have IQ score differences between two groups that are simply the result of the test errors showing a difference where no actual difference exists. IQ tests are often also very frequently administered incorrectly or scored incorrectly even if correctly administered, magnifying the size of the error band around the obtained score. For this study, I'm not sure if the human subjects tested were tested by test-givers who were "blind" to what group the test-takers were in, which could also be an issue.

innguest 12y ago
> All mainstream individual IQ tests have been scored this way for just about all of my lifetime. Correct me if I'm wrong but I thought the Cattell tests were obviously scored in the Cattell scale (24 s.d.) and the Stanford-Binet tests in the Binet scale (16 s.d.). When I was into reading about psychometrics it seemed to me that the cut off percentile was a more straightforward way to talk about IQ than using either of those three scales (Wechsler, Binet, Cattell).
- tokenadult 12y ago
  The current Stanford-Binet test (and the next one, which is in preparation) use the typical 15 points per standard deviation scoring. The Cattell test is not a "mainstream" IQ test and correlates rather poorly with expected variables that ought to correlate well with IQ like academic achievement. Standard scores by the current definition are readily converted to percentile ranks by look-up tables, by the definition of standard deviation assuming a roughly normal distribution. As above, it's important to note that there is error in any IQ test. I've now had a chance to read the underlying papers related to this thread (which go back at least to 2008), and the IQ tests used in this study are even less mainstream than I feared. "A total of 240 individuals were evaluated with the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and the Wisconsin Card Sorting Test (WCST)." doi:10.1016/j.bbi.2008.04.156

TrainedMonkey 12y ago

That is true, but we can't translate 10% longer time taken on performing some task into 10% less effective IQ.

duaneb 12y ago
No, but there aren't really any good parameters for IQ, and time taken is a damn good, reliable, objective measure.
- TrainedMonkey 12y ago
  Yes, but without knowing standard deviations and mean time taken for both groups we can't do math and claim any likelihood of observed result occurring in a random distribution.

leeber 12y ago

Guys, we're programmers here not statisticians: def test(): ... n1 = numpy.average(numpy.random.normal(100,15,52)) ... n2 = numpy.average(numpy.random.normal(100,15,40)) ... return abs(n1-n2) / ((n1+n2)/2.0) ... >>> vals = [test() for i in xrange(0,1000)] >>> numOver10 = len([v for v in vals if v > .1]) >>> numOver10 2

tomrod 12y ago
Crucial in your code is the standard deviation of 15. Where is that coming from? Ah, I see. Standard IQ normalizations.
- leeber 12y ago
  http://en.wikipedia.org/wiki/Intelligence_quotient http://en.wikipedia.org/wiki/Intelligence_quotient