[Rasch] Models of unidimensional constructs havetheirlimitations:what is a "good thing"?

Paul Barrett pbarrett at hoganassessments.com
Fri Nov 9 06:15:55 EST 2007


	From: rasch-bounces at acer.edu.au
[mailto:rasch-bounces at acer.edu.au] On Behalf Of Stephanou, Andrew
	Sent: Thursday, November 08, 2007 4:58 PM
	To: Agustin Tristan
	Cc: rasch at acer.edu.au
	Subject: RE: [Rasch] Models of unidimensional constructs
havetheirlimitations:what is a "good thing"?
	... Social scientists illude themselves if they think that
reading ability is a more complex construct than the construct of

Do social scientists delude themselves?
Is there a definition of the construct of "reading ability", which
stands independent of the method of its measurement, or are the rules
for measurement also partially constituent of the meaning of the
construct? I'm assuming the former .. but ... 
With regard to reading ability, is it possible to be able to read text
without comprehending what is being read? Is that "reading ability" or
something else? I note in the paper 
(2006) Reading ability mediates the relationship between education and
executive function tasks. Journal of the International
Neuropsychological Society , 12, 64-71.
Reading ability is measured by (p. 65) the 

"Wide Range Achievement Test-3 (WRAT-3): Reading (Wilkinson, 1993)

This is a test of word familiarity and sight reading ability involving
the pronunciation of a series of 15 letters of the alphabet and 42
increasingly difficult words. A maximum score of 57 is possible. As
reported in Spreen and Strauss (1998), it has been useful in estimating
premorbid intelligence, and moderately relates to WAIS-R IQ scores
(Griffin et al., 2002). " 
The abstract rom the paper reads ...
Neuropsychological test results are affected by multiple factors, but
usually age and education are the only variables by which norms are
stratified. Some authors have questioned whether these variables alone
are sufficient (e.g., Marcopulos et al., 1997; Manly et al., 2002),
since such norms have lead to problems, such as poor specificity for
African Americans on dementia screening devices (Fillenbaum et al.,
1990). Recent research has shown that reading ability, a measure of
educational quality, attenuated racial differences in test performance
(Manly et al., 2002). We specifically examined whether reading ability
would account for a greater amount of variance than education in
executive function tests in a population traditionally subject to poor
educational quality. Results determined that reading ability accounted
for a significantly greater amount of variance than years of education
for Letter-Number Sequencing, Similarities, COWA, Trail Making Test, and
Coloured Progressive Matrices. Reading ability was found to
significantly mediate the relationship between each of these tests and
Then there is the paper by 
van den Bos, K. P; Nakken, H; Nicolay, P. G; & van Houten, E. J.(2007)
Adults with mild intellectual disabilities: Can their reading
comprehension ability be improved? Journal of Intellectual Disability
Research. Vol 51(11) Nov 2007, 835-849 (which doesn't use Lexiles by the
Are we talking about an ability or a skill, or are these terms
Is reading ability actually a behavioral proxy for vocabulary knowledge?
What is comprehension, is it reading ability or another variable which
requires separate measurement?
Look at the corresponding definition of temperature; Giancoli (1988)
defines it as:
"how hot or cold an object is" .. (p. 406) and on page 449 "Temperature
is a measure of the average kinetic energy of individual molecules"
where on page 449, heat is defined as referring to: "the amount of
energy transferred from a hot body to a cold body" 
Howerver, defining "energy" is not so simple!
Perhaps reading ability is as complex as defining "temperature" - when
"average kinetic energy of molecules" is unpacked for meaning?  Maybe
even more so when that heady mix of "variables" like comprehension,
sight/phonic reading (without comprehension), vocabulary, and reasoning
are all taken to be constitutive somehow of the observed "reading
Or, do you claim that the Lexile system alone now defines (by its
application) the construct "reading ability"? I would guess Andrew
Kyngdon might want to make some statements here also.!
Regards .. Paul
Giancoli, D.C. (1988) Physics for Scientists and Engineers with Modern
Physics. 2nd Edition. Prentice-Hall. 


Paul Barrett, Ph.D.

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Chief Research Scientist

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