[Rasch] formative v. reflective measures in assessment research
dbacon at du.edu
Sun Oct 27 02:00:44 EST 2013
Hi all --
To offer more explanation on my reflective v. formative question, in reflective measurement models, the construct/latent trait causes the measures/indicators/items, whereas in formative models, the measures cause the latent trait. Jarvis, MacKenzie and Podsakoff (J Consumer Research, 2003) offer a thorough description of this difference. They cite Bollen and Lennox (Psych Bull, 1991) as identifying the same distinction, except that Bollen and Lennox call reflective indicators 'effects indicators' in a principal component model, and formative indicators 'causal indicators' in a composite latent construct model.
Jarvis et al. cite a formative example from Crosby and Stephens (1987) that I will paraphrase here. In measuring the construct "personal contact with life insurance agents", suppose the following measures are used:
I was contacted by my agent to make changes in my policy
I was contacted by my agent to sell me more life insurance
I was contacted by my agent to describe new insurance offerings
I was contacted by my agent to keep my policy in place
In these items, the agent would not suggest keeping the policy and changing the policy, so the inter-item correlations here should be low or perhaps even negative, yet all of these statements indicate personal contact. Internal consistency is not necessary for formative measures; to assess the quality of formative measures we need to look at criterion-related validity. Thus, formative models are a bit more like regression models, where the many independent variables are assumed to have no error and may have low intercorrrelations but the one dependent variable does have error.
Jarvis et al. go on to report how measurement models have often been misspecified, even in top marketing journals, as formative measures have been treated as reflective and vice versa. They show how such misspecification can bias structural path estimates.
Getting back to Rasch measurement, it seems to me that Rasch assumes a reflective/effects/principal components model. However, Rasch may occasionally be misapplied to formative indicators. In the latter case, model fit and internal consistency would probably be low, but this is due mainly to fundamental model misspecification. Or can Rasch be used with formative indicators?
Has this type of model misspecification been discussed in the Rasch literature? More specifically, are all tests of ability or knowledge generally reflective models? Is there a good cite that someone can point me too?
Thanks for any insights you may be able to provide.
From: rasch-bounces at acer.edu.au [mailto:rasch-bounces at acer.edu.au] On Behalf Of Bond, Trevor
Sent: Saturday, October 26, 2013 1:17 AM
To: rasch at acer.edu.au
Subject: Re: [Rasch] formative v. reflective measures in assessment research
Perhaps you could share what you mean by formative and reflective, so we might be able better to answer your question.
From: Donald Bacon <dbacon at du.edu<mailto:dbacon at du.edu>>
Reply-To: "rasch at acer.edu.au<mailto:rasch at acer.edu.au>" <rasch at acer.edu.au<mailto:rasch at acer.edu.au>>
Date: Saturday, 26 October 2013 3:57 AM
To: "rasch at acer.edu.au<mailto:rasch at acer.edu.au>" <rasch at acer.edu.au<mailto:rasch at acer.edu.au>>
Subject: [Rasch] formative v. reflective measures in assessment research
Hi all -
The Rasch model assumes that each measure in a scale reflects the same underlying trait, and so it seems that a reflective measurement model is appropriate, and internal consistency is a desirable quality. But what about the case of a long comprehensive exam, such as one we might use for assessment. In my experience, these exams often behave as if they were close to unidimensional, even though many different learning outcomes are captured. If well designed, these tests often exhibit high internal consistency. Because the models fit well, I've always thought of the measures as reflective, but perhaps my theory is wrong even though the fit is good; maybe the measures are formative. Is there any way to use the Rasch model with formative indicators?
Thanks for any insights you might have -
Donald R. Bacon, Ph.D.
Professor of Marketing
Editor, Journal of Marketing Education
Daniels College of Business
University of Denver
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