[Rasch] fit analysis / rating scale dilemma (please help)
gstone at UTNet.UToledo.Edu
Mon Jun 5 09:53:40 EST 2006
There is NEVER any justification for "No opinion" as a middle point on a rating scale. If indeed the respondent has no opinion, then they will not, cannot or choose not to participate in the data gathering process. It is ironic that after so much evidence supporting the use of even numbered rating scales and the idea that "no opinion" is not a theoretically justifiable midpoint, this continues to arise. Why would no opinion be the theoretical midpoint of a scale? Even if the scale ran from say "strongly disagree to strongly agree" a middlepoint would still not suggest the lack of an opinion. While some have considered "no opinion" to mean "half and half" that is dubious. Either way, it fails to assist us in understanding their likes, beliefs, etc. as it provides us with no difference.
The only justification for its use is as a comfortable "out" for those who cannot, will not or choose not to answer the question. For those who wish to give participants this out, it must be done with the understanding that it will be considered as missing data during the analysis.
The justification you seek is not necessary. What IS necessary is for those who continue to promote this notion to justify, explain and defend the theoretically unjustifiable opinion that the lack of a feeling/belief/opinion is the midpoint along a scale ranging from very negative to very positive, etc. We work so hard to create constructs within Rasch and they are defined so beautifully. Should we not expect the same level of clarity from the rating scale?
Gregory E. Stone, Ph.D., M.A.
Assistant Professor of Research and Measurement
The University of Toledo, Mailstop #923
Toledo, OH 43606 419-530-7224
Editorial Board, Journal of Applied Measurement www.jampress.org
For information about the Research and Measurement Programs at The University of Toledo and careers in psychometrics, statistics and evaluation, email gregory.stone at utoledo.edu.
From: rasch-bounces at acer.edu.au on behalf of Mary A Coleman/AC/VCU
Sent: Sun 6/4/2006 11:15 AM
To: rasch at acer.edu.au
Subject: [Rasch] fit analysis / rating scale dilemma (please help)
I am analyzing a 5 question, 5 point likert-type scale where 3 is labeled no opinion (N= 1054). There is no missing data.
Mean square fit statistics for items are good, but the standardized stats for three items are bad (outfit standardized MNSQs of 3.8, -2.9, -5.4). I have ordered threshold/structure measures and the category probability curves look nearly perfect. When I treat the 3 category as missing, the fit stats improve ( .3, -2.6, -4.2), and the structure measures/category probability curves don't suffer.
I've read the literature which justifies treating the "No opinion" category as missing, but generally, it is reported only within the context of disordered structure measures.
I guess I am seeking some feedback/justification for treating "no opinion" responses as missing data given that the scale seems to be functioning or for keeping the item with a standardized outfit of 3.8.
Mary Angela Coleman
Virginia Commonwealth University
colemanma at vcu.edu
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