Infrastructure for psychometric modeling such as data classes (for item response data and paired comparisons), basic model fitting functions (for Bradley-Terry, Rasch, parametric logistic IRT, generalized partial credit, rating scale, multinomial processing tree models), extractor functions for different types of parameters (item, person, threshold, discrimination, guessing, upper asymptotes), unified inference and visualizations, and various datasets for illustration. Intended as a common lightweight and efficient toolbox for psychometric modeling and a common building block for fitting psychometric mixture models in package "psychomix" and trees based on psychometric models in package "psychotree".
Changes in Version 0.5-0
o Infrastructure for IRT modeling in the unified "psychotools" framework is extended by marginal maximum likelihood (MML) estimation of generalized partial credit models and parametric logistic models, respectively. The corresponding fitting functions (see below for details) call mirt() or multipleGroup() from the "mirt" package but return objects for which all standard extractor methods (item parameters, person parameters, etc.) and visualization methods (item response curves, parameter profiles, person-item maps, etc.) are available.
o The new gpcmodel() function interfaces mirt (see above) and fits (generalized) partial credit models (GPCMs) by MML.
o The new plmodel() function interfaces mirt (see above) and fits various parametric IRT logistic models using MML: 1PL (Rasch), 2PL, 3PL, 3PLu, and 4PL.
o New functions and eponymous classes guesspar(), and upperpar() to extract/represent so-called guessing parameters and upper asymptote parameters of IRT models.
o personpar() now distinguishes between parameters of the assumed person ability distribution (personwise = FALSE) and the individual person parameters for each person/subject in the underlying data set (personwise = TRUE). In the CML case, the latter simply computes the raw score for each person and then extracts the corresponding person parameter. In the MML case, this necessitates (numerically) integrating out the individual person parameters (also known as factor scores or latent trait estimates) based on the underlying normal distribution.
o Added new data set "ConspiracistBeliefs2016" from the Open Source Psychometrics Project (2016).
o Added new simulated data set "Sim3PL" for fitting dichotomous IRT models, especially the 3PL and 3PLu.
Changes in Version 0.4-3
o Conditionally register all estfun() and bread() S3 methods for model objects, provided that the "sandwich" package is attached.
o Added native routine registration for esf.c.
o Use R version of elementary_symmetric_functions() by default on Win/i386 due to small numeric differences on that platform.
o The estfun() method for "btmodel" objects always computed the scores with the last object for the reference category - even if a different ref= was specified in the model. Thanks to Heather Turner for pointing out the problem.
o The itempar() method for "btmodel" objects miscomputed the variance covariance matrix (unless the first object was used as the ref when estimating the model). Thanks to Heather Turner for pointing out the problem.
Changes in Version 0.4-2
o Added new data set "PairClustering" from Klauer (2006).
o Fixed replication code in example of StereotypeThreat (reported by Ed Merkle).
o Basil Abou El-Komboz changed his name to Basil Komboz.
Changes in Version 0.4-1
o Properly imported grDevices and utils in NAMESPACE.
o Added new item response data set MathExam14W with esponses of 729 students to 13 items in a written exam of introductory mathematics along with several covariates.
Changes in Version 0.4-0
o New function mptmodel() and corresponding extractor functions for fitting multinomial processing tree (MPT) models. These functions are somewhat experimental, and their user interface might change in future releases.
o Bug fix in itempar() method for "raschmodel" objects if alias = FALSE. In the previous version the methods had an erroneous trailing NA.
o Improved item names labeling in plot() method for "itemresp" objects to conform with regionplot() function for IRT models.
o mscale<-() method for "itemresp" has been improved so that categories can be easily collapsed (e.g., dichotomized).
Changes in Version 0.3-0
o Infrastructure for IRT modeling in "psychotools" is greatly enhanced. Therefore the main modeling functions are now called raschmodel() for Rasch models, rsmodel() for rating scale models, pcmodel() for partial credit models, and btmodel() for Bradley-Terry models. The old *.fit() functions from previous versions of the package still exist but now internally call the new *model() functions. Also, the classes returned have the same names as the *model functions.
o A unified visualization framework for fitted IRT models has been added: For all types of models (Rasch, RSM, PCM) one can visualize profiles of the item parameters, regions for the most likely response, item or category characteristic curves, item information, and person-item plots. All of these rely on the unified framework for extracting parameters and predictions (see below).
o New functions and eponymous classes itempar(), threshpar(), and discrpar() to extract/represent item, threshold, and discrimination parameters of item response models. Methods for the IRT models (Rasch, RSM, PCM) are provided. In addition, several methods for standard generic functions (print(), coef(), vcov()) are available.
o The worth() generic now internally calls the methods for itempar().
o Estimation of person parameters for a given item response model is now available via the generic function personpar(). Specific methods for Rasch, rating scale and partial credit models allow the estimatation of person parameters via joint maximum likelihood estimation. Methods for standard generic functions (print(), coef(), vcov()) are available for the resulting objects of class "personpar".
o predict() methods for Rasch, rating scale and partial credit models have been added. For a given fitted model object, these can be used to predict various types of response probabilities or actual reponses.
o New functions anchor() and anchortest() provide a variety of anchor methods for the detection of uniform differential item functioning (DIF) between two pre-specified groups in the Rasch model. To test for DIF, the itemwise Wald test is implemented.
o itemresp() is the class constructor for responses of n subjects to k items which can be polytomous and have different measurement scales. A wide range of methods to standard generics is provided as well as to generics created for the "paircomp" class. Thus, features can be easily extracted/replaced, summaries/visualizations can be produced, subsetting/merging/etc. is facilitated.
o The handling of argument 'ref' when producing a region plot (previously called effect plot) was changed. Whereas in the previous implementation, the restriction specified in this argument was applied to the cumulative absolute item threshold parameters, it now is applied to the absolute item threshold parameters.
o A bug occuring in pcmodel() when null categories are present and nullcats = "keep" was fixed. (Thanks to Oliver Prosperi for reporting this.)
o The processing of the minimal category zero in the function rsmodel() was changed. Only if for all items, the minimal category is above zero, downcoding takes place. Otherwise, the missing minimal categories are treated as not observed, i.e., with a frequency of zero.
Changes in Version 0.2-0
o Major update with new model fitting functions (partial credit and rating scale model) and improved infrastructure for conditional maximum likelihood estimation (C implementation of elementary symmetric functions).
o Partial credit models (PCMs) can be fitted with the function PCModel.fit(). The interface and return value is similar to that of RaschModel.fit().
o Rating scale models (RSMs) can be fitted with the function RSModel.fit(). The interface and return value is similar to that of RaschModel.fit() and PCModel.fit().
o The function elementary_symmetric_functions() for computing ESFs is extended and now part of the exported user interface. The R implementation for binary items up to order 2 is complemented by a C implementation for both binary and polytomous items up to order 1.
o Due to numerical instabilities in the coefficients and standard errors between different architectures, the optimization method for Rasch/RSModel/PCModel.fit() was changed from nlm(...) to optim(..., method = "BFGS"). Consequently, the arguments "reltol" and "maxit" are used now instead of "gradtol" and "iterlim". For backward compatibility RaschModel.fit() still supports the old arguments but might cease to do so in future releases.
Changes in Version 0.1-4
o Added YouthGratitude data from Froh, Fan, Emmons, Bono, Huebner, Watkins (2011, PA), provided by Jeff Froh and Jinyan Fan. Some approximate replication code is provided in the examples (the parts depending on lavaan are in \dontrun).
Changes in Version 0.1-3
o Fully exported elementary_symmetric_functions(). (An extended C implementation is under development and will be included in future releases.)
Changes in Version 0.1-2
o Support of non-integer weights in btReg.fit(). To facilitate this, summary.paircomp() gained a weights argument so that optionally the weights are aggregated instead of observations counted.
o Actually pass on nlm() arguments from RaschModel.fit(). Also support iterlim = 0, i.e., set up model at pre-specified parameters.
o Added StereotypeThreat data from Wicherts, Conor, Hessen (2005, JPSP), provided by Jelte M. Wicherts. Replication code is provided in the examples (the parts depending on lavaan are in \dontrun).
Changes in Version 0.1-1
o New "psychotools" package containing all 'base' infrastructure previously contained in "psychotree". This is in order to provide both methods and data that can be reused by "psychotree" and the new package "psychomix" (as well as potentially further packages).
o Classes: "paircomp" and associated methods.
o Models: btReg.fit() and RaschModel.fit() and associated methods.
o Data: Firstnames, GermanParties2009, Soundquality (previoulsy in psychotree) and VerbalAggression (new data, contained in other formatting in difR/verbal and lme4/VerbAgg).