## Saturday, April 19, 2014

### Why composite scores are more extreme than the average of their parts [feedly]

The brilliance of Dr. Joel Schneider

----
Why composite scores are more extreme than the average of their parts
// Assessing Psyche, Engaging Gauss, Seeking Sophia

Suppose that two tests have a correlation of 0.6. On both tests an individual obtained an index score of 130, which is 2 standard deviations above the mean. If both tests are combined, what is the composite score?

Our intuition is that if both tests are 130, the composite score is also 130. Unfortunately, taking the average is incorrect. In this example, the composite score is actually 134. How is it possible that the composite is higher than both of the scores?

If I measure the length of a board twice or if I take the temperature of a sick child twice, the average of the results is probably the best estimate of the quantity I am measuring. Why can't I do this with standard scores?

Standard scores do not behave like many of our most familiar units of measurement. Degrees Celsius have meaning in reference to a standard, the temperature at which water freezes at sea level. In contrast, standard scores do not have meaning compared to some absolute standard. Instead, the meaning of a standard score derives from its position in the population distribution. One way to describe the position of a score is its distance from the population mean. The size of this distance is then compared to the standard deviation, which is how far scores typically are from the population mean (more precisely, the standard deviation is the square root of the average squared distance from the mean). Thus, the "standard" to which standard scores are compared are the mean and standard deviation.

An index score of 130 is 2 standard deviations above the mean of 100.

The average of two imperfectly correlated index scores is not an index score. Its standard deviation is smaller than 15 and thus our sense of what index scores mean does not apply to the average to two index scores. To make sense of the composite score, we must convert it into an index score that has a standard deviation of 15.

$\dfrac{(130+130-2*100)}{\sqrt{2+2*0.6}}+100\approx 134$

How is this possible. It is unusual for someone to score 130. It is even more unusual for someone to score 130 on two tests that are imperfectly correlated. The less correlated the tests, the more unusual it is to score high on both tests.

Below is a geometric representation of this phenomenon. Correlated tests can be graphed with oblique axes (as is done in factor analyses with oblique rotations). The cosine of the correlation is the angle between the axes. As seen below, the lower the correlation, the more extreme the composite. As the correlation approaches 1, the composite approaches the average of the scores.

The lower the correlation, the more extreme the composite score.

In a previous post, I presented this material in greater detail.

----

## Thursday, April 3, 2014

### Sharing A Flynn effect among deaf boys in Saudi Arabia via BrowZine

A Flynn effect among deaf boys in Saudi Arabia
Bakhiet, Salah eldin Farah Attallah; Barakat, Serry Mohammed Roshdy; Lynn, Richard
Intelligence, Vol. 44 – 2014: 75 - 77

10.1016/j.intell.2014.03.003

## Tuesday, April 1, 2014

### \"Revisiting intellectual disability and the death penalty\" in APA Monitor - April 2014

I found "Revisiting intellectual disability and the death penalty" in Monitor - April 2014
 April 2014

Monitor - April 2014

I thought you would enjoy "Revisiting intellectual disability and the death penalty" from Monitor - April 2014

Click the thumbnail or here to go to the issue.

If you cannot click on the links, paste this link into a browser:
http://www.apamonitor-digital.org/apamonitor/201404/?pg=0&pm=0&u1=friend&article_id=409379

## Friday, March 7, 2014

### The TIme Doc...one of the other hats I wear :)

Click on "read more" box under my picture

The Tempo Times | March 2014: Brain Health Edition
 Home | Provider Login | IM University | IM-Home | eClinic

Register for an IM Course at the low price:

$149  Date Location 3/8 Las Vegas, NV 3/15 Reading, PA 3/22 Jersey City, NJ 3/22 Seattle, WA 3/29 Carrollton, GA 3/29 Chicago, IL 4/5 Albany, NY 4/5 Columbia, SC 4/5 Dallas, TX 4/5 Inverness, FL 4/12 Boston, MA 4/12 Long Beach, CA 4/12 Long Island, NY 4/12 Wichita, KS This symbol indicates an Advanced Pediatric Course following the scheduled IM Certification Course. This symbol indicates an Advanced Adult Course following the scheduled IM Certification Course.  REGISTER NOW › We are looking for Webinar Presenters! Get compensated for sharing your IM knowledge with other providers! We are looking for presentations for 2014. Click here to submit a description. If your presentation is accepted, you will receive$350 upon completion of the your live webinar presentation.

Meet March's Professional of the Month:
Dr. Kevin McGrew

Dr. Kevin McGrew, the Time Doc, is a member of the IM scientific advisory board and a strong advocate for the importance of better neural timing. In addition to co-authoring the fourth edition of the Woodcock-Johnson battery (WJ IV), he is the Director of the Institute for Applied Psychometrics (IAP), the Research Director for the Woodcock-Muñoz Foundation (WMF) and a visiting professor in Educational Psychology at the University of Minnesota, where he received his doctoral degree in the same field. Dr. McGrew clearly understands how to use his time wisely. After spending 12 years as a school psychologist, and another 10 as a professor of Applied Psychology, Dr. McGrew switched his focus to research. He has published over 70 articles, books and book chapters in his areas of expertise and maintains IQ's Corner blog and the Mindhub®. Look for Dr. McGrew in our upcoming IM demo video where he explains the importance of getting your brain and body in sync.

 Read more in our blog... ›

Friendly Fire: A Look at Multiple Sclerosis (MS)

Multiple Sclerosis (MS) is a chronic, unpredictable condition that can rob individuals of their ability to live a normal, healthy life. Since lesions and plaque scars appear on multiple areas of brain matter, the severity and symptoms vary drastically. While some people my live a full, happy life with very few interruptions, others have their life cut short by a malignantly progressive form of the disease. With IM, you don't just adapt to MS, you can slow the progression and actually regain functional mobility. Today, we look at some of the symptoms of MS, treatment options, and the success of Margaret, a MS sufferer who uses IM to stay mobile and active.

 Read more in our blog... ›

IM-Home Tips and Motivational Strategies

In case you missed our free webinar in January, we wanted to share some of the great tips for using Interactive Metronome® (IM) at home. IM-Home lets users train in the comfort and privacy of their own home while still receiving Provider-supervised IM training. It's time to take the clinic to your clients! IM-Home is also great for children looking for an edge in the classroom, athletes who want an advantage on the field and adults who want to excel professionally.

 Read more in our blog... ›

Upcoming Webinars

 ▪ Effects of IM training on soccer skill performance in a sample of female elite soccer players This webinar is based on a large study on elite female soccer players, investigating the effects of timing-training (IM) on soccer-specific skills. It will have emphasis on the effects of IM training on the performance of a number of soccer-specific skills (cross-pass, shot for goal and heading), but will also address some of the customized IM-exercises used, and the reasoning behind the choice of these specific exercises. Moreover, the webinar will include some preliminary analyses of brain activation patterns (fMRI) before and after IM training. Here, we have investigated if the internal / cognitive representations of an observed action may change as an effect of IM training. Date: 5/28/14 Time: 12:30 pm EST Price: \$15 CEUS: AOTA 0.1, BOC 1.0, PTs & PTAs may submit paperwork to your state board
 Register Now ›

 This email was sent to iapsych@charter.net why did I get this?    unsubscribe from this list    update subscription preferences Interactive Metronome · 13798 NW 4th Street · Suite 300 · Sunrise, FL 33325 · USA

## Wednesday, March 5, 2014

### Article: New evidence confirms link between IQ and brain cortex

This study was previously posted, with comments, at my ICDP blog, where a link is provided to an annotated copy of the article.

******************************************************
Kevin McGrew, PhD
Educational Psychologist
Director, Institute for Applied Psychometrics
IAP
******************************************************

## Tuesday, March 4, 2014

### Article: The g beyond Spearman's g: Flynn's paradoxes resolved using four exploratory meta-analyses

The g beyond Spearman's g: Flynn's paradoxes resolved using four exploratory meta-analyses
http://www.sciencedirect.com/science/article/pii/S0160289614000105

Sent via Flipboard

## Monday, March 3, 2014

### Fwd: SCOTUSblog

The notable SCOTUSblog's analysis of today's Atkins arguments (Hall v Florida)..see first story

SCOTUSblog