mrsmith Yellowbellied Woodpecker
Joined: Jul 01, 2011 Posts: 63

Posted: Tue Nov 27, 2012 9:43 am Post subject: NVLD  Where does the 15 point limit come from? (Rewritten) 


NVLD is often defined as VIQPIQ beeing over 15 points.
Where does this limit come from? (1)
Is it a practical limit for classroom NVLD, or is it more like a tipping point for a wide range of problems?
Is it a lower limit (2a), with perhaps some additional criteria needing to be satisfied, or is it more like a tipping point, where the population size corresponds to the population with a higher difference, but some below does have it and some above does not have it?(2b)
Is PIQ (rather that NVIQ for example), used because it is most important in the classrom, or because it is more predictive of wider problems.
If 2b : I am aware that more specific problems can lead do diagnosis below the limit. Is this factored into the limit?
Confusing first version
NVLD is often defined as the PIQ beeing in the lower 2.5% percentile of the population compared to the VIQ.
Where does this limit come from?
Is it a practical limit for classroom NVLD, or is it more like a tipping point for a wide range of problems?
(Like is the difference between 2.3 and 2.7 quite big compared to the difference between 2.7 and 3.1?)
Valentine
Last edited by mrsmith on Thu Nov 29, 2012 9:22 am; edited 10 times in total 

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1000Knives It's not difficult if you know how.
Joined: Jul 09, 2011 Age: 23 Posts: 5079 Location: CT, USA

Posted: Tue Nov 27, 2012 10:34 am Post subject: 


I've not heard those limits. I've heard it's more described by PIQ to VIQ gap. I've heard a 15 point gap between your VIQ and PIQ is enough to satisfy diagnostic criteria. In my case, my gap is around 50 points. My PIQ is like 80, and my VIQ is like 130+. So it's rather severe NVLD, I guess. But I think officially, it starts at 15 point gap. 

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mrsmith Yellowbellied Woodpecker
Joined: Jul 01, 2011 Posts: 63

Posted: Tue Nov 27, 2012 11:44 am Post subject: It comes from 2 standard deviations 


1000Knives wrote:  I've not heard those limits. I've heard it's more described by PIQ to VIQ gap. I've heard a 15 point gap 
It comes from 2 standard deviations, which I think corresponds to a certain point difference the way the IQ scale is defined.
(I think 15points is 1 stdev  corresponding to the 15% percentile).
I think it is better to think of it in terms of percentiles  You can compare it to the 1% who has ASD or the numbers for ADHD. 

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Ravenclawgurl Phoenix
Joined: Jun 20, 2007 Posts: 1307 Location: somewhere over the rainbow

Posted: Tue Nov 27, 2012 11:45 am Post subject: 


but what about in the weschler children scale 4 which doesnt have performance and verbal iq its divided into 4 parts? 

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OddDuckNash99 Hypercoaster
Joined: Nov 16, 2006 Posts: 2678

Posted: Tue Nov 27, 2012 1:08 pm Post subject: 


The definition of NVLD as a neuropsychiatric condition was first described by Dr. Bryan Rourke. Statistically speaking, though, yes, the VIQ/PIQ split comes from standard deviation for the WAIS. 15 points is 1 standard deviation, and a 15point difference between VIQ and PIQ (where VIQ is larger) is the baseline definition for NVLD. The "four parts" Ravenclawgurl mentions are subscores, from which VIQ, PIQ, and FSIQ (VIQ + PIQ average) are determined. On the WAIS (I don't know much about the WISC), Vocabulary and Working Memory are used to determine VIQ, and Perceptual Organization and Processing Speed are used to determine PIQ.
Also, in order to qualify for an NVLD diagnosis, you needn't have a PIQ that is in the lowest 2%, which is 2 standard deviations from the mean of 100. (Thus, a PIQ of 85 or below.) You just need to have a VIQ/PIQ split that is a statistically significant difference (i.e., 15+ points). For example, I have NVLD, but my PIQ is 116, which is in the "highaverage" range. My VIQ is 134 ("very superior" range), which is 17 points higher than my PIQ. Even though my PIQ is +1 SD from the mean of 100, I still have NVLD due to the incongruence between my PIQ and VIQ.
For NVLD, the subscores sometimes are an even better determinant of the learning disorder. Working Memory, used for VIQ, involves Digit Span and Arithmetic sections, both of which have numbers. Plus, Vocabulary is an entirely verbal/languagebased score, and Perceptual Organization is an entirely visualspatial score. I feel my NVLD staggered abilities are best shown by these two subscores: My Vocabulary score is 140 (almost +2 SD above mean), and my Perceptual Organization score is 105 ("average" range). That's a 35point difference, compared to just 17 points for VIQ vs. PIQ. _________________ Helinger: Now, what do you see, John?
Nash: Recognition...
Helinger: Well, try seeing accomplishment!
Nash: Is there a difference? 

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Ravenclawgurl Phoenix
Joined: Jun 20, 2007 Posts: 1307 Location: somewhere over the rainbow

Posted: Tue Nov 27, 2012 2:12 pm Post subject: 


OddDuckNash99 wrote:  The definition of NVLD as a neuropsychiatric condition was first described by Dr. Bryan Rourke. Statistically speaking, though, yes, the VIQ/PIQ split comes from standard deviation for the WAIS. 15 points is 1 standard deviation, and a 15point difference between VIQ and PIQ (where VIQ is larger) is the baseline definition for NVLD. The "four parts" Ravenclawgurl mentions are subscores, from which VIQ, PIQ, and FSIQ (VIQ + PIQ average) are determined. On the WAIS (I don't know much about the WISC), Vocabulary and Working Memory are used to determine VIQ, and Perceptual Organization and Processing Speed are used to determine PIQ.

well if thats thats how they determine performance iq with the processing speed then i likely have nvld because my processing speed score was so low it was in the MR range 

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mrsmith Yellowbellied Woodpecker
Joined: Jul 01, 2011 Posts: 63

Posted: Tue Nov 27, 2012 2:27 pm Post subject: 


OddDuckNash99 wrote:  The definition of NVLD as a neuropsychiatric condition was first described by Dr. Bryan Rourke. Statistically speaking, though, yes, the VIQ/PIQ split comes from standard deviation for the WAIS. 15 points is 1 standard deviation, and a 15point difference between VIQ and PIQ (where VIQ is larger) is the baseline definition for NVLD. 
I have Googled a bit, and I generally see the 1 stdev limit
That would correspond to 15% of the population, which much really be far to high, so it must be some additional filtering going on?
The only prevalence numbers I have seen are 23%, which corresponds to 2 stdevs. 

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OddDuckNash99 Hypercoaster
Joined: Nov 16, 2006 Posts: 2678

Posted: Tue Nov 27, 2012 3:29 pm Post subject: 


mrsmith wrote:  That would correspond to 15% of the population, which much really be far to high, so it must be some additional filtering going on?
The only prevalence numbers I have seen are 23%, which corresponds to 2 stdevs. 
No, 15 points for 1 SD doesn't mean 15% of the population. The way that a standard normal curve works is that ~68% of people lie within +/ 1 SD of the mean (in this case, 100). And 96% of people lie within +/ 2 SDs of the mean. So, only 2% of the population have an IQ of 130 or above (+2 SDs), and only 2% of the population have an IQ below 85 (2 SDs).
It also isn't true that having greater than or equal to 1 SD between your VIQ and PIQ scores is equivalent to having a PIQ score that is greater than or equal to 1 SD below the mean. As I showed above, my PIQ is 1 SD above the mean, but I still have NVLD, due to its relationship to my VIQ score. Now, I'm sure that most NVLDers out there do have a PIQ in the 8090 range; I realize that I am not a typical case. (I am fortunate enough to have taught myself certain visualspatial skills over the years.) But again, it is possible to have NVLD with any level PIQ score, so long as it is 15+ points lower than the VIQ score.
As far as prevalence rates of NVLD, what I commonly read is that NVLD makes up around 110% of all total learning disorders. It's not all that common, even in the learning disorder category, but again, that statistic doesn't refer to specific IQ scores.
And in response to Ravenclawgurl, Symbol Coding/Processing Speed is only one component of PIQ. Block Design, Matrices, and other tests also are factored in for PIQ. Having low Processing Speed doesn't necessarily mean NVLD. I scored extremely highly in Processing Speed, yet I have NVLD. _________________ Helinger: Now, what do you see, John?
Nash: Recognition...
Helinger: Well, try seeing accomplishment!
Nash: Is there a difference? 

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Ravenclawgurl Phoenix
Joined: Jun 20, 2007 Posts: 1307 Location: somewhere over the rainbow

Posted: Tue Nov 27, 2012 3:42 pm Post subject: 


yeah but what i mean im sure the processing speed numbers bring the rest of the performance iq down 

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mrsmith Yellowbellied Woodpecker
Joined: Jul 01, 2011 Posts: 63

Posted: Tue Nov 27, 2012 3:56 pm Post subject: 


OddDuckNash99 wrote: 
No, 15 points for 1 SD doesn't mean 15% of the population. The way that a standard normal curve works is that ~68% of people lie within +/ 1 SD. 
I didn't say that. If 68.2% is within, 31.8 % is outside, or 15.9% is on each side. 

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OddDuckNash99 Hypercoaster
Joined: Nov 16, 2006 Posts: 2678

Posted: Tue Nov 27, 2012 4:03 pm Post subject: 


mrsmith wrote:  I didn't say that. If 68.2% is within, 31.8 % is outside, or 15.9% is on each side. 
Okay, I see what you meant now. But it still doesn't mean that people who qualify as having NVLD will necessarily have a PIQ score that is in that 15% below 100. _________________ Helinger: Now, what do you see, John?
Nash: Recognition...
Helinger: Well, try seeing accomplishment!
Nash: Is there a difference? 

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mrsmith Yellowbellied Woodpecker
Joined: Jul 01, 2011 Posts: 63

Posted: Tue Nov 27, 2012 4:28 pm Post subject: 


OddDuckNash99 wrote:  mrsmith wrote:  I didn't say that. If 68.2% is within, 31.8 % is outside, or 15.9% is on each side. 
Okay, I see what you meant now. But it still doesn't mean that people who qualify as having NVLD will necessarily have a PIQ score that is in that 15% below 100. 
If scores are above 100% you can't say that you have a LD or that you are impaired from the scores alone.
(But when I wrote OP, I though the limit was sharper, and that it was more significant) 

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btbnnyr Rabbit In Cat's Clothing
Joined: May 19, 2011 Posts: 4269 Location: Lost Angleles Carmen Santiago

Posted: Tue Nov 27, 2012 4:57 pm Post subject: 


What if someone has a 140 PIQ and 155 VIQ? This person still has NVLD, a learning disorder? 

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OddDuckNash99 Hypercoaster
Joined: Nov 16, 2006 Posts: 2678

Posted: Wed Nov 28, 2012 8:21 am Post subject: 


btbnnyr wrote:  What if someone has a 140 PIQ and 155 VIQ? This person still has NVLD, a learning disorder? 
By definition, yes. No matter how high or how low a person's IQ, there should not be more than a 10point difference between VIQ and PIQ. Obviously, the higher the IQ scores, the less a person will struggle, but they still will experience learning difficulties compared to their potential. The fictional case you described, for instance, probably wouldn't experience many struggles, but their PIQ would still be limited in reference to what their PIQ abilties SHOULD be.
Somebody with these high of scores probably wouldn't ever need to go get tested for a learning disorder due to compensatory strategies, but they still would have staggered abilities. Again, using myself as an example, I never was tested for a learning disorder as a child. I only took an IQ test and was diagnosed with NVLD in college. Because my PIQ abilties are higher, I was able to "get by" in math classes using compensatory strategies, such as my "photographic" memory. But even though I was able to be in honors math courses and get "A"s for the most part, math always has been a huge struggle for me. And teachers never understood why somebody as seemingly "smart" as I struggled so much with math. So, it's sort of a doubleedged sword. If you have a higher PIQ to begin with, yes, you are fortunate enough to (most likely) achieve greater academic success for longer, but the downside is that your very real struggles are much more puzzling to teachers and people in general. It's a lot like how there are obvious advantages to being highfunctioning on the spectrum, but there also are disadvantages (it's a "hidden" disability). _________________ Helinger: Now, what do you see, John?
Nash: Recognition...
Helinger: Well, try seeing accomplishment!
Nash: Is there a difference? 

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mrsmith Yellowbellied Woodpecker
Joined: Jul 01, 2011 Posts: 63

Posted: Wed Nov 28, 2012 8:43 am Post subject: 


OddDuckNash99 wrote:  btbnnyr wrote:  What if someone has a 140 PIQ and 155 VIQ? This person still has NVLD, a learning disorder? 
By definition, yes.. 
If the point criteria is met by 15% of the population, it should mean that only 1/3 of those that "have NVLD".
Depending on the diagnostic criteria you can imagine it makes some difference in the chance that you pass.
One other post on this forum says it should then rather be called a "learning style" than "learning disability",
but AFIAK the term NVLD is used even if all scores are high.
Another thing is that the point difference perhaps should be different at a high IQ. 

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