Gifted Issues Discussion homepage Forums Identification, Testing & Assessment how is FSIQ calculated

Can someone tell me how is Full Scale IQ calculated from the from the IQ scores of the subsets? i.e VC index, WM index et.c

Thank You.

You have to have a manual to look it up in a table. It is not an average of the other indices.

Do you have this table? Where can I get this table?

Thanks

You can get it here - for a minimum of $1069.

The FSIQ is determined by the sum of the scaled scores from the 10 subtests of the WISC (each subtest's scaled score can range from 1-19, higher if extended norms are used; the scaled scores are NOT the same as the composite scores that have a mean of 100). So, if you have the sum of scaled scores (or can calculate it if a tester provided the 10 subtest scaled scores) you may be able to figure out the FSIQ by looking for the same scaled score elsewhere on this board. Many people have posted WISC scores including both the sum of scaled scores and the corresponding FSIQ. So if you find a sum of scaled scores that matches yours, you have the FSIQ.


The following table won't be useful for 99.9% of the population, but the FSIQ equivalents using extended norms are available in the WISC Technical Report #7 (link below). Of course, these only apply to kids that needed the extended norms and have a sum of scaled scores greater than 167 (which corresponds to an FSIQ of 150 or higher), but just in case you are looking in that range, here is the link:

http://www.pearsonassessments.com/N...C-8E4A114F7E1F/0/WISCIV_TechReport_7.pdf

It's probably propietary/confidential, but may be deduced from many examples of posted scores.

Hmmm. I’ve been thinking about the conversion of the Sum of Scaled Scores to the FSIQ (I have nothing better to do while I sit around waiting for trick-or-treaters) and I am very surprised I can’t find this information online. Granted I am a statistician, but it didn’t take me long to figure out how one would statistically calculate an FSIQ from the Sum of Scaled Scores. I would think this calculation would be available online somewhere. Is it really possible for this information to be proprietary?

I also don’t know why a psychologist would keep the FSIQ out of a WISC report. I personally think it should be included, even if the GAI is a better indication of an individual’s giftedness (although this should be mentioned in the report). Do some psychologists refuse to give this information even when it is requested?

Pi22, as a parent of a child who has had it NOT calculated that was a really really good thing for us, when you have a 3-4 deviation spread between indexes the FSIQ is meaningless but educators WILL look at if it's there and many will not think any further, no matter how many notes the psychologist makes about it's meaningless nature.

MumOfThree, I think you have an excellent point that educators may not be able to look past the FSIQ. It is a shame that educators aren't better trained in understanding the results. My own DS has a 60 point spread (4 standard deviations) between index scores so I do understand the importance of the four indexes, but I also wanted to know his FSIQ since working memory and processing speed are still aspects of general intelligence. So I wouldn't say the FSIQ was meaningless to us.

I'm pretty sure that most of the people who administer the tests don't know how to do the calculation. The whole test is proprietry so I would guess the tables and the computer calculation programme are included in that. I don't suppose that means the calculation as such is propriety - just the manner of use.

Actually, the calculation of the FSIQ from the Sum of Scaled Scores isn't magical (nor proprietary). No table is required as there is a simple one-to-one correspondence between the Sum of Scaled Scores and the FSIQ. It would be the same as someone calculating the Percentile Rank from a Composite Score. It is just basic statistics.

FSIQ = 25 + 0.75*S where S is the Sum of Scaled Scores.

Here's the statistical reasoning for anyone interested...

The Sum of Scaled Scores is the sum of the 10 Subtest Scaled Scores. Each Subtest Scaled Score ranges from 1-19 with a mean of 10 and a standard deviation of 3. Each is assumed to be normally distributed. The Sum of Scaled Scores follows a normal distribution with a mean of 100 and a standard deviation of 20. The only difference between the Sum of Scaled Scores and the FSIQ is that the FSIQ has a standard deviation of 15 (not 20). You can easily convert from one normal distribution to another, so if you know the Sum of Scaled Scores, you know the Fulll Scale Composite Score (FSIQ):

FSIQ = 100 + ((15/20)*(S-100)) <- same as above, before simplication

The 100's are the means of the two distributions and the 15 and 20 are their standard deviations. All of this can be obtained by publically released information.

Please show me the thread where these scores are posted. The ratings where as follows.

Verbal Comprehension Index Very Superior
Perceptual Reasoning Index Very Superior
Working Memory Index High Average
Processing Speed Index Superior

You're right of course even with a big spread it does, to some extent, give you an idea of likely "performance-in-a-classroom" potential (as compared to actual reasoning ability).

Can you show me where some of those threads are?

Verbal Comprehension Index Very Superior
Perceptual Reasoning Index Very Superior
Working Memory Index High Average
Processing Speed Index Superior

Here are the composite scores associated with the classification labels:

Very Superior: >= 130
Superior: 120-129
High Average: 110-119
Average: 90-109
Low Average: 80-89
Borderline: 70-79

And the GAI gives you an idea of likely "performance-in-a-classroom potential" if the teachers accommodate any issues that may be impacting processing speed and working memory. That's why it's so important that educators understand the importance of all the composite scores. Maybe someday they will (wishful thinking, I know).

indeed.

Thanks so much that.

Do you have a table which I could use to estimate the subset scores based on index given? for VCI, WMI et.c

Question for StatGuru,

Thank you so much for the info about calculating FISQ from WISC IV scaled scores.
Would you please be able to tell me how that works for the WISC V with a mean of 70?

Actually, it's not quite as simple as has been portrayed above. There is a table for calculating the FSIQ on the WISC-V, and it doesn't equate quite as easily to the mean of the Index scores. In addition to updated norms, the WISC-V is somewhat different from the WISC-IV on several levels (5 indices vs 4, different weighting of cognitive areas, different tasks feeding into the indices, etc.). With regard to the FSIQ, there is a notable difference that arises from the inclusion of only 7 subtests, rather than the 10 used for calculation of the 5 primary index scores.

Based on the mean index score you report, you may wish to seek further clarification from the professional who completed the evaluation, as that range is likely to be out of the experience of most of the posters on this forum.

pm'd you.

I'm not a professional, just the parent of a 2e student with a significant spread in scores due to lower processing speed and somewhat lower working memory. Our neuropsych did calculate FSIQ for our ds in spite of the large gap, but fwiw, I don't see how it is helpful at all in understanding our ds. While processing speed and working memory are components of what is considered to be "general intelligence", having the FSIQ doesn't help understand our child's learning strengths or challenges - it's simply a somewhat-averaged calculation between widely varying scores that represent different areas of abilities. What was useful to me as a parent in understanding my ds' abilities was having all the subscores and the composite scores for various categories such as VCI etc. What was useful in advocating at school was his GAI and achievement testing.

Best wishes,

polarbear

Hi aeh,

Thanks for thinking along.

Earlier in this old thread, StatGuru explains how to to calculate the FSIQ for the WISC IV from the the sum of the scaled scores using this formula

FSIQ = 25 + 0.75*S where S is the Sum of Scaled Scores.

(And he/she explained: "The Sum of Scaled Scores is the sum of the 10 Subtest Scaled Scores. Each Subtest Scaled Score ranges from 1-19 with a mean of 10 and a standard deviation of 3. Each is assumed to be normally distributed. The Sum of Scaled Scores follows a normal distribution with a mean of 100 and a standard deviation of 20. The only difference between the Sum of Scaled Scores and the FSIQ is that the FSIQ has a standard deviation of 15 (not 20). You can easily convert from one normal distribution to another, so if you know the Sum of Scaled Scores, you know the Full Scale Composite Score (FSIQ):
FSIQ = 100 + ((15/20)*(S-100)) <- same as above, before simplication
The 100's are the means of the two distributions and the 15 and 20 are their standard deviations. All of this can be obtained by publically released information.)

I would like to know how to calculate a FSIQ from the sums of the scaled scores on the WISC V. Basically, because I was wondering what FSIQ a sum of scaled scores of 114 on WISC V would translate to.)

bananagirl, pm'd you.

I ended back on this board, once again, because I'm trying to calculate IQ scores. I think this is why I ended up here in the first place.

Does anyone know how to calculate the Verbal IQ using the VCI and WMI using the WAIS-IV?

And, if so, is there some kind of source that I can link to?

The VIQ was not developed for the WAIS-IV, as more contemporary theories of intelligence (plus stats) found that the four-factor solution (VCI, PRI, WMI, PSI) was a better representation of the standardization data set. So there's no way to compute a VIQ with validity.

For your statistical entertainment, here's an article comparing various models for confirmatory factor analysis of the WAIS-IV:
https://pdfs.semanticscholar.org/55a4/44255cf1a07acf94135cfa055ea3e2bbfec7.pdf

Hello I have the same question

Same as which specific question from above?