Fits Rasch models (RM), linear logistic test models (LLTM), rating scale model (RSM), linear rating scale models (LRSM), partial credit models (PCM), and linear partial credit models (LPCM). Missing values are allowed in the data matrix. Additional features are the ML estimation of the person parameters, Andersen's LR-test, item-specific Wald test, Martin-Loef-Test, nonparametric Monte-Carlo Tests, itemfit and personfit statistics including infit and outfit measures, ICC and other plots, automated stepwise item elimination, simulation module for various binary data matrices.
News for Package 'eRm'
Changes in Version 0.15-6:
� 'plotGOF()': added arguments 'x_axis', 'y_axis', 'set_par', and 'reset_par' to ease customization of the plot.
� Imports functions from default packages packages, as required by the new CRAN-check.
Changes in Version 0.15-5:
� implemented an 'anova()' method for all models (except LLRAs, which have their own: 'anova.llra'). see '?anova.eRm'
� added a function to compute separation reliability, as proposed in Wright & Stone (1999; see '?SepRel').
� 'plotINFO()' accepts more arguments via '...' (see '?plotINFO').
� fixed a bug in 'plotPWmap()'.
� fixed a bug in the internal function 'get_item_cats()' related to 'NA's (affecting LLRA and item-information functions).
� switched encoding to UTF-8 to avoid problems with diacritics, etc. (e.g., Martin-L�f).
� updated citations.
� general improvements.
Changes in Version 0.15-4:
� streamlining some functions, updating the vignette, etc.
� warnings are now treated more consistently and can be suppressed with 'suppressWarnings()'
� the 'plotGOF()' function was revamped and tidied up in a couple of places, e.g.:
� the plotting order of elements in a non-interactive call has been changed to put confidence ellipses and lines in the background and text in the foreground. � the x- and y-limits are now dynamically computed by default, so that confidence regions and ellipses are inside the plotting region. � the leading "'I'" before item numbers has been removed for better legibility.
� moved 'NEWS' to the new fancy 'NEWS.Rd' file/format
Changes in eRm version 0.15-3:
� an error in 'test_info()' was fixed.
� 'eRm' now depends on 'R' >= 3.0.0
Changes in eRm version 0.15-2:
� an error in 'Tpbis.stat' was fixed.
Changes in eRm version 0.15-1:
� a bug in 'person.parameter()' has been fixed that caused the estimation to crash in some cases.
� a bug in 'thresholds()' has been fixed that caused the routine to crash.
Changes in eRm version 0.15-0:
� the 'RaschSampler' package has been merged into 'eRm' for convenience (still available as a separate package).
Changes in eRm version 0.14-5:
� the package is now byte-compiled by default.
� some statistics added to 'NPtest()', 'T7' and 'T7a' removed.
� fixed a bug in 'plotPWmap()'.
� fixed the 'mplot' argument in plotting routines.
� fixed the split-criterion '"all.r"' in 'LRtest()'.
� deleted all usages of 'data()' in examples, since eRm uses "lazy data."
Changes in eRm version 0.14-4:
� when calling 'NPtest()', the 'RaschSampler' can now be controlled more specifically ('burn_in', 'step', 'seed').
� various improvements and bugfixes for LLRA-related functions.
� person parameter values can be extracted now for all persons using 'coef()'. Additionally, in-/exclusion of extrapolated values (for 0 and perfect scores) can be controlled via the argument 'extrapolated'.
� LRtest now computes standard errors ('se = TRUE') by default.
� plotDIF now plots "difficulties" for all models (formerly, "easiness" parameters were plotted for Rasch models).
Changes in eRm version 0.14-3:
� minor bug fixed in 'plotGOF()', where on rare occasions confidence ellipses were plotted together with control lines (spotted by Peter Parker)
� improved labelling in 'plotjointICC()'
Changes in eRm version 0.14-2:
� warning regarding group assignment when using median or mean split removed from 'MLoef()'
� modification in 'NPtest()' to split long output lines
� changed the delimiters of 'plotDIF()' confidence intervals to 'pch = 20' (small bullet).
Changes in eRm version 0.14-1:
� new experimental functions to calculate and plot item and test information (by Thomas Rusch)
� bug fixed in the calculation of item and person Infit t and Outfit t (hint from Rainer Alexandrowicz).
� 'eRm' no longer depends on the 'RaschSampler' package. However, it must be installed to use 'NPtest()'.
� changed the delimiters of 'plotDIF()' confidence intervals to 'pch = 20'.
Changes in eRm version 0.14-0:
� new (wrapper) function 'LLRA()' for fitting linear logistic models with relaxed assumptions including utilities for preparing data ('llra.datprep()'), setting up ('build_W()') and modifying ('collapse_W()') design matrices, comparing LLRA models ('anova()') and plotting results ('plotTR()' and 'plotGR()') (by Thomas Rusch).
� "exact" version of the Martin-L�f test for binary items and arbitrary splits added as method to 'NPtest()'.
� in 'plotGOF()' confidence ellipses can now be drawn for subsets of items, optionally using different colours
� new function 'plotDIF()' (by Kathrin Gruber): plots confidence intervals for item parameters estimated separately in subgroups, uses LR objects as input
� adapted the 'MLoef()' function to work with polytomous data and more than two item groups
� error checks in NPtest:
0/full responses for items meaningless for NPtest,
group in 'method = "T4"' must be of type logical,
specifying all items for T4 gives meaningless results.
� warning regarding group assignment when using median split removed from 'LRtest()' and 'Waldtest()'.
� some modifications in 'plotPWmap()': horizontal plotting, different default plotting symbols, option to change size of plotting symbols
� bug in 'MLoef()' fixed (now using logs in calculating the person contributions)
� 'eRm' now depends on 'R' >= 2.12.0
� Latin1 encoding removed
� bug in 'plotICC()' (always same title) fixed
Changes in eRm version 0.13-0:
� 'LLTM()', 'LRSM()', and 'LPCM()' work now for repeated measurement designs with treatment groups and missing values.
� Rename vignette to "eRm".
Changes in eRm version 0.12-2:
� new function 'plotPWmap()' to plot Bond-and-Fox style pathway maps for the data by Julian Gilbey. Since calculation of the t-statistics requires calculation of the kurtosis of the standardized residuals, according changes to 'itemfit.ppar()', 'personfit.ppar()', 'pifit.internal()', 'print.ifit()', and 'print.pfit()'.
� 'plotPImap()' patched by Julian Gilbey: length of 'item.subset' did not match the documentation, warning stars did not all appear, pre-calculated person.parameter data can be passed to the function via pp, mis-ordered items can be coloured. some minor bugs fixed.
� the optimizer can be changed to 'optim()' using 'fitctrl <- "optim"' and reset to 'nlm()' (the default) with 'fitctrl <- "nlm"'
� value of 'LRtest()' now contains the list 'fitobj' which contains the model objects according to the subgroups specified by 'splitcr'
� 'MLoef()' no longer supports missing values
Changes in eRm version 0.12-1:
� function invalid from package 'gtools' integrated into 'eRm'. 'eRm' no longer depends on 'gtools'.
Changes in eRm version 0.12-0:
� for 'RM()', 'RSM()', and 'PCM()': eta parameters are now displayed as difficulty parameters; 'print()' and 'summary()' methods changed accordingly.
� new labeling of eta parameters in 'RM()', 'RSM()', and 'PCM()'. they now are labeled according to the estimated parameters for items ('RM()'), items + categories ('RSM()'), items x categories ('PCM()')
� function 'MLoef()' for Martin-L�f-Test added
� 'df' in 'personfit()' and 'itemfit()' corrected
� the 'logLik()' functions now extract the log-likelhood and df into objects of class '"logLik.eRm"' and '"loglik.ppar"' with elements 'loglik' and 'df'. the corresponding print methods have been modified accordingly.
� method 'coef.ppar()' to extract person parameter estimates added
� option for beta parameters added to coef.eRm
� in confint.eRm: default 'parm = "beta"'
� minor modifications in the help file for 'IC()'
� 'plotPImap()': revised rug added, bug concerning 'item.subset' fixed, minor modifications to enhance readability
� minor modifications in 'plotjointICC()': allows for main title and colors, option 'legpos = FALSE' suppresses legends, dev.new removed, 'legend = FALSE' produced incorrect labeling
� minor modifications in 'plotICC()': allows for main title and colors, default coloring with 'col = NULL' instead of 'NA' for compatibility, option 'legpos = FALSE' suppresses legends, 'mplot' is now 'FALSE' if only one item is specified
� plot.ppar: dev.new removed
� option "visible" in print.ifit und print.pfit to allow for avoiding overly long output and for extraction of infit and outfit values (maybe changed to a coef method later)
� 'strwrap()' for NPtest print methods to break long lines
� new methods 'IC.default()' and 'pmat.default()' for enhanced error messages
� lazy loading package and datafiles