plotDIF | R Documentation |
Performs an plot of item parameter conficence intervals based on LRtest
subgroup splitting.
plotDIF(object, item.subset = NULL, gamma = 0.95, main = NULL,
xlim = NULL, xlab = " ", ylab=" ", col = NULL,
distance, splitnames=NULL, leg = FALSE, legpos="bottomleft", ...)
object |
An object of class |
item.subset |
Subset of items to be plotted. Either a numeric vector indicating the items or a character vector indicating the itemnames. If nothing is defined (default), all items are plotted. |
gamma |
The level for the item parameter's confidence limits (default is gamma = 0.95). |
main |
Main title for the plot. |
xlim |
Numeric vector of length 2, giving the x coordinates ranges of the plot (the y coordinates depend on the number of depicted items). |
xlab |
Label for the x axis. |
ylab |
Label for the y axis. |
col |
By default the color for the drawn confidence lines is determined automatically whereas every group (split criterion) is depicted in the same color. |
distance |
Distance between each item's confidence lines – if omitted, the distance shrinks with increasing numbers of split criteria. Can be overriden using values in (0, 0.5). |
splitnames |
For labeling the splitobjects in the legend (returns a nicer output). |
leg |
If |
legpos |
Position of the legend with possible values |
... |
Further options to be passed to |
If there are items that cannot be estimated for some reasons, certainly these ones are not plotted.
For plotting several objects of class LR
, the subgroup splitting by LRtest
has to
be carried out for the same data set (or at least item subsets of it).
Plotting a certain subset of items could be useful if the objects of class LR
contain a huge number
of estimated items.
The default level for the conficence limits is gamma = 0.95. (If the conficence limits should be corrected it is useful to use a correction, e.g., Bonferroni: 1 - (1 - gamma) / number of estimated items.)
plotCI
returns a list containing the confidence limits of each group in each LRtest
object.
Kathrin Gruber, Reinhold Hatzinger
LRtest
, confint.threshold
, thresholds
# the object used is the result of running RM(raschdat1)
res <- raschdat1_RM_fitted # see ? raschdat1_RM_fitted
## Not run:
# LR-test on dichotomous Rasch model with user-defined split
splitvec <- rep(1:2, each = 50)
lrres <- LRtest(res, splitcr = splitvec)
# LR-test with mean split
lrres2 <- LRtest(res, split = "mean")
# combination of LRtest-objects in a list
RMplotCI <- list(lrres, lrres2)
## End(Not run)
# the object raschdat1_RM_plotDIF is the result of the computations outlined
# above and is loaded to save computation time. see ?raschdat1_RM_plotDIF
RMplotCI <- raschdat1_RM_plotDIF
# Confidence intervals plot with default assumptions
plotDIF(RMplotCI)
# Confidence intervals plot with Bonferroni correction
plotDIF(RMplotCI, gamma = (1 - (0.05/10)))
# Confidence intervals plot for an item subset
plotDIF(RMplotCI, item.subset = 1:6)
# with user defined group color and legend
plotDIF(RMplotCI, col = c("red", "blue"), leg = TRUE, legpos = "bottomright")
# with names for the splitobjects
plotDIF(RMplotCI, col = c("red", "blue"), leg = TRUE, legpos = "bottomright",
splitnames = c(paste("User", 1:2), paste(rep("Mean", 2), 1:2)))
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