[R] start.val in GRM (ltm package)
Jeff
r at jp.pair.com
Thu Jul 19 20:38:04 CEST 2012
Can someone please give me an example of how to enter starting values for a
GRM (IRT) model using the ltm package?
The instructions from the ltm manual are below, but when I create either a
list of the values or a matrix I get the error, "start.val not of proper
type." I can find no example on the web other than using NULL or Random,
which won't work for me.
The code I'm using looks something like this:
row1 <- c(0.146, 1.505, 2.158)
row2 <- c(4.124, 5.790, 1.589)
row3 <- c(3.635, 4.916, 1.426)
startval_list <- c( row1 , row2 , row3)
Results <- grm( DelT4 , constrained = FALSE, start.val = startval_list)
...which produces the error mentioned above.
Manual instructions:
start.val -
a list of starting values or the character string "random" . If a list, each
one of
its elements corresponds to each item and should contain a numeric vector
with
initial values for the extremity parameters and discrimination parameter;
even if
constrained = TRUE the discrimination parameter should be provided for all
the items. If "random" random starting values are computed.
Thanks
Jeff
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