[R] Inserting weights in ltm package

Thomas Lumley tlumley at uw.edu
Wed Jul 27 05:44:02 CEST 2011

On Wed, Jul 27, 2011 at 2:58 PM, Erica Crome <erica.crome at mq.edu.au> wrote:
> Afternoon R help,
> I want to run Rasch/IRT analyses using the ltm package, however, I am
> using large scale survey data which requires weighting for accurate
> results. I attempted to create a weighted object to insert into the
> formulae of the ltm packages, however, the survey data only includes
> 30 replicate weights and a sampling weight. The svrepdesign requires
> additional information  such as jacknife weights in an external object
> (for scale, rscale), however, I do not have these. I typically just
> use the sampling weight when doing analyses in other platforms such as
> MPlus, however there does not appear to a way of referring to this
> directly in the ltm formulae.
> My question is: am I able to insert sampling weights directly into an
> ltm analysis, or is there a way of creating a weighted data object
> with the information available which I could then insert into the ltm
> analyses? I have been unable to find any similar help topics using the
> websearch. Thanks.

You can easily use svrepdesign() to create a weighted survey design
object using the replicate weights, but that won't help you. The
functions in the ltm package do not appear to accept any sort of
weights.  I don't know enough about those models to know if simple
weighting would be enough or whether pairwise sampling probabilities
would be needed as they are for linear mixed models.


Thomas Lumley
Professor of Biostatistics
University of Auckland

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