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    #173389 - 10/31/13 11:48 PM Re: how is FSIQ calculated [Re: fsiqcalculate]
    StatGuru Offline
    New Member

    Registered: 10/31/13
    Posts: 1
    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.



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    #173390 - 11/01/13 12:12 AM Re: how is FSIQ calculated [Re: Pi22]
    fsiqcalculate Offline
    Junior Member

    Registered: 10/31/13
    Posts: 5
    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


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    #173391 - 11/01/13 12:16 AM Re: how is FSIQ calculated [Re: fsiqcalculate]
    MumOfThree Offline
    Member

    Registered: 04/07/11
    Posts: 1567
    Loc: Australia
    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).

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    #173392 - 11/01/13 01:02 AM Re: how is FSIQ calculated [Re: Pi22]
    fsiqcalculate Offline
    Junior Member

    Registered: 10/31/13
    Posts: 5
    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


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    #173399 - 11/01/13 05:36 AM Re: how is FSIQ calculated [Re: fsiqcalculate]
    Pi22 Offline
    Junior Member

    Registered: 12/30/12
    Posts: 45
    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



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    #173400 - 11/01/13 05:45 AM Re: how is FSIQ calculated [Re: MumOfThree]
    Pi22 Offline
    Junior Member

    Registered: 12/30/12
    Posts: 45
    Originally Posted By: MumOfThree
    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).

    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).

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    #173482 - 11/01/13 03:06 PM Re: how is FSIQ calculated [Re: fsiqcalculate]
    MumOfThree Offline
    Member

    Registered: 04/07/11
    Posts: 1567
    Loc: Australia
    indeed.

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    #173498 - 11/01/13 08:40 PM Re: how is FSIQ calculated [Re: StatGuru]
    fsiqcalculate Offline
    Junior Member

    Registered: 10/31/13
    Posts: 5
    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

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    #238923 - 06/20/17 08:13 PM Re: how is FSIQ calculated [Re: fsiqcalculate]
    BananaGirl Offline
    Junior Member

    Registered: 06/15/17
    Posts: 9
    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?

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    #238937 - 06/22/17 10:43 AM Re: how is FSIQ calculated [Re: fsiqcalculate]
    aeh Offline
    Member

    Registered: 04/26/14
    Posts: 3556
    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.

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