A rough estimate of the values of the latent variable ("ability"). The sum
scores (number of correct responses) are ranked, breaking ties at random.
The ranks are divided by the sample size + 1, and the corresponding
quantiles of the standard Normal distribution are returned. Used as default
in the non-parametric IRF plots produced by npp in analogy to
Jim Ramsay's TestGraf. Another possible use is in itf.
Usage
qrs(resp)
Arguments
resp
A matrix of responses: persons as rows, items as columns,
entries are either 0 or 1, no missing data