Chi-square difference test using WLSMV PreviousNext
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 Jennifer Hartwig posted on Tuesday, April 18, 2006 - 8:35 am
I am conducting a CFA using categorical (binary) variables (54 items) using WLSMV. I am attempting to evaluate the fit of 3 different models:

Model 1 consists of a general factor.

Model 2 is a two-factor model (based on item format: MC versus student-produced response items)

Model 3 is a four-factor model based on content areas.

My questions pertain to conducting a Chi-square difference test between Models 1 & 2 and Models 1 & 3:

1) I tried to use the command "DIFFTEST", but received an
error message indicating that my "models were not nested." Is there another method I can use to compare model fit?

2) I am unclear as to why my models are not nested. It seems as though both Model 2 and Model 3 would be nested in Model 1 (separately). I am using all 54 items in all three models.

Please advise.
Jennifer
 Linda K. Muthen posted on Tuesday, April 18, 2006 - 1:02 pm
Model 1 is nested in models 2 and 3. You may have your setup backwards. You should run model 1 last. If you are doing this and still having problems, send your input, data, output, and license number to support@statmodel.com.
 Ruth Parslow posted on Sunday, January 21, 2007 - 7:56 pm
I am using DIFFTEST with WLMSV to compare the goodness of fit of 3 models based on 17 categorical items. (There are some theoretical reasons for comparing these different models.) In the first model the 17 all load on 1 factor; in the second model, 9 items are on 1 factor and 8 on a second. In the third model, also with 2 factors, 7 of the original 9 load on the first factor while the remaining 2 of Factor 1 now load on the second factor in addition to the 7 already specified in the second model. Is there any way I can compare the Goodness of fit between the second and third models since the message I get is that these are not nested. Can I use the difference between the two Chi-square difference measures, the first from comparing Models 1 and 2 and the second from comparing Models 1 and 3 as a further Chisquare difference measure?

Thanks
Ruth
 Linda K. Muthen posted on Monday, January 22, 2007 - 8:40 am
Your second and third models are not nested so using a difference test to compare their fit is not appropriate.
 Sanja Franic posted on Wednesday, November 18, 2009 - 5:26 am
I cannot use the "difftest" option in MPlus when also using the "model constraint" option. Is there any other way to calculate the chi-square difference, given that I am using the WLSMV estimator?
Thanks,
Sanja
 Sanja Franic posted on Wednesday, November 18, 2009 - 6:05 am
I think I just found the answer to my own question. I use WLSM instead of WLSMV and use the scaling correction factors I get in the output to perform a shi-sq difference test.
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