Hi Chris,
the formula should be
cbind(v1, v2, v3,...,vLast)~NULL,
*you need to list all varible names corresponding to the respondents
that you are interested
instead of using m~NULL
right now in Zeligalized item response type of model, the formula has
to be in form of 'cbind(...)~NULL', and the 'data' option has to be
specified. A more user friendly version of formula call is being
incorporated into Zelig.
hope this helps.
Ying
Quoting Chris Bergstresser <chris(a)subtlety.com>om>:
Hi all --
I'm following the instructions in trying to run a 1-dimensional IRT
model from some NES data. It's pretty simple, I've got a data.frame
that has the respondents in rows and the variables in columns. But,
the IRT model requires subjects in columns, so I first do:
m = as.data.frame(t(vars));
... this gives me a new data.frame, with respondents in columns and
the variables in rows. I should, I think, be able to run the model
like so:
z.out <- zelig(m ~ NULL, model = "irt1d", data = m);
... but I get an error:
Error in model.frame(formula, rownames, variables, varnames, extras,
extranames, :
invalid variable type for 'm'
All of the variables are numeric, with scattered "NA"s. I'm not sure
why I get the error, and I'm also curious why the "data" argument is
manditory, since I'm not referencing any variables that aren't in the
global namespace already.
Can anyone enlighten me?
-- Chris
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