[Rasch] Units of measurement in the social sciences

Stephen Humphry shumphry at cyllene.uwa.edu.au
Mon Oct 22 12:40:34 EST 2007


Hi Anthony, yes it is relevant. You may also be interested to know  
what Thurstone said on this point. He characterized the fundamental  
role of the unit in his early work, as follows.

"
we shall see that it is possible to compare the discriminal  
dispersions for two stimuli and to determine experimentally the ratio  
of any two of these dispersions. Psychological measurement depends,  
then, on the adoption of one of these dispersions as a base and the  
use of its standard deviation as a unit of measurement for the  
psychological continuum under investigation." (Thurstone, 1959, p. 24)

Thurstone (1959, p. 24) also said "There is, of course, no further  
unit in terms of which this standard deviation can be expressed.  It  
is itself a unit of measurement 
".

Due to the relationship between the dichotomous Rasch model and case 5  
of Thurstone's 'law' of comparative judgment (e.g. Andrich, 1978),  
Thurstone's comments apply equally to the Rasch model.

Regards,

Steve



Andrich, D. (1978). Relationships between the Thurstone and Rasch  
approaches to item scaling. Applied Psychological Measurement, 2,  
449-460

Thurstone, L.L. (1959). The Measurement of Values. Chicago: The  
University of Chicago Press.




Quoting Anthony James <luckyantonio2003 at yahoo.com>:

> regarding my question I found something which seems relevent:
>   http://rasch.org/rmt/rmt32b.htm
>
> Anthony James <luckyantonio2003 at yahoo.com> wrote:
>     Dear folks,
>   Another dumb question...
>   I'll be grateful for any comments.
>   When we are talking about "units of measurement" in the physical   
> sciences we are talking about some tangible things. (I avoide the   
> word "concrete" because I know you don't like it in this context and  
>  argue that all measures are abstractions). However, I mean kilo or   
> meter , for example, are understandable attributes that have a   
> concerete existence. A "sample meter" ,i.e., a rod of 1 meter can be  
>  aligned with any object and count the number of alignments. Or we   
> can put some potatos on the pan of a scale and put enough weaights   
> on the other pan until the beam is balanced.
>
>   1. How does the Rasch model make this "sample meter" or the   
> one-kilo weight to compare the performance of the students against?
>   2. Whose performance  is considered as the unit and how is it constructed?
>   3. What's the defenition of a logit?
>
>   Cheers
>   Anthony
>
>
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