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Chun Wang posted on Thursday, August 01, 2013 - 7:09 pm
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We are trying to estimate parameters of a hierarchical IRT model in Mplus as follows: th_{ikt} = lamb * th_{i0t} + e1_{ikt} th_{ikt} ~ item_{1, ikt} ... item_{J, ikt} We tried the following code: ... VARIABLE: NAMES ARE it1-it40; CATEGORICAL ARE it1-it40; ANALYSIS: TYPE = GENERAL; ESTIMATOR = MLR; LINK = LOGIT; MODEL: th1 BY it1-it20* (p1-p20); th2 BY it21-it40* (p21-p40); th0 BY th1-th2* (lamb); th1-th2@.5 [th1-th2@0]; [th0@0]; th0@1; .... But constraining [th0@0] and th0@1 is not what we want! We want to freely estimate those parameters while constraining mean(threshold) = 0, var (threshold) = 1, and th1-th2@*.5 (ev) such that ev = 1-lamb^2 (i.e., constrain the residual variance). We tried adding a model constraint line for the latter: MODEL: th1-th2@*.5 (ev); MODEL CONSTRAINT: ev = 1-lamb^2; but Mplus complained and forced all of the item loadings to be 1. We would appreciate if you could give us some advice on this issue. |
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