npp {irtoys} | R Documentation |
A plotting routine producing non-parametric analogues of the IRF
not unlike those in Jim Ramsay's TestGraf program.
The curves are produced by a kernel binomial regression of
the actual responses to an item on some estimates of the
latent variable, by courtesy of package sm
.
npp(resp, x, items, from = -4, to = 4, co = 1, main = "Non-parametric response function", add = FALSE, bands = FALSE, label = FALSE)
resp |
A matrix of responses: persons as rows, items as columns, entries are either 0 or 1, no missing data |
x |
The values of the latent variable ("ability") for the same persons whose responses are given in resp . If not given, function qrs will be plugged in, which is the approach of TestGraf |
items |
An index to the items (columns of resp ) to be shown on the plot. If not given, all items will be plotted. |
from |
Lower limit for ability on the plot. Default is -4. |
to |
Upper limit for ability on the plot. Default is 4. |
add |
When add=T , the curve is added to a plot, otherwise a new plot is started. Default is F. |
main |
The main title of the plot, given that add=F . |
co |
The colour of the curves. Default is 1 for black. Use co=NA to plot each curve in a different colour. |
bands |
When bands=T , confidence bands are added. |
label |
When label=T , individual curves will be labeled with the item number. |
Ivailo Partchev
James O. Ramsay (2000). TestGraf: A program for the graphical analysis of multiple choice test and questionnaire data. McGill University, Montreal, Canada
data(Scored) p.2pl <- est(Scored, model="2PL", engine="ltm") # plot items 1:5 in different colours, label npp(Scored, items=1:5, co=NA, label=TRUE) # For item 7, compare npp with the 2PL parametric IRF npp(Scored, items=7, bands=TRUE) plot(irf(ip=p.2pl[7,]), co=3, add=TRUE)