I am attempting to use a LCA with knownclass and categorical variables to estimate an IRT model with vertical equating. The following syntax achieves that goal, however, I would like mplus to NOT estimate the items with asterisks next to them in the syntax below for certain groups. In other words, I would like i1 to be constrained to equality across groups 1,3, and 4, but to not be estimated for group 2. Constraining the threshold and loading to 0 does not appear to work because a threshold of 0 is meaningful in the IRT framework.
VARIABLE: Names are i1-i61 year; usevariables are i1-i6; categorical are i1-i6; classes = g(4); knownclass = g (year = 1 year = 2 year = 3 year = 4);
Perhaps by saying "not be estimated for group 2" you would like those items to be missing in group 2 so that their information in that group is not used? If so, you can give them a missing data flag in that group.
Jamie Tock posted on Thursday, February 22, 2018 - 6:57 am
I would like that their information is not used but I am not sure how I would use a missing data flag in the multiple group situation. Typically, I could say: Missing = i1(-99) However, this would refer to i1 in all groups. I would like the data to be declared missing for only one of the four groups (i.e. for item 1 in group 2).
Jamie Tock posted on Thursday, February 22, 2018 - 7:10 am
Additionally, is there a way to do a multiple group analysis and estimate an item for one group but not others? For example, if I wanted to estimate item i1 for groups 1, 3, and 4, but not include i1 in group 2. Setting the item thresholds and loadings to 0 will not work because 0 is meaningful in the IRT context.