        **************************************************
        *                                                *
        *  Changes and Developments in the difR Package  *
        *                                                *
        **************************************************



------------------------------------
- Changes in difR 3.3 (2010-10-21) -
------------------------------------

MAJOR UPDATES

  o  It is now possible to cature and save the output of each
     DIF method directly from the 'dif...' functions. The 
     arguments 'save.output' and 'output' control for saving
     the output (as displayed by the corresponding 'print.'
     function) into a text file, whose name and path are
     specified within the 'output' argument.

  o  The functions 'selectDif', 'selectGenDif', 'dichoDif'
     and 'genDichoDif' have been adapted in order to allow
     for saving their output too

  o  Similarly, the plots drawn from the 'plot.' functions can
     be captured into either PDF or JPEG format, by using the
     newly added 'save.plot' and 'save.options' arguments.
     They define the name of the figure, the path where it is
     saved, and the format of the figure.

  o  In addition, the 'print.' functions display a message to
     specify whether the output was saved (and where the saved
     file is located) or not, and the 'plot.' functions display
     a message into the R console to specify whether the plot 
     was not captured, the format is incorrect, or the plot was 
     captured and where it was stored.


MINOR UPDATES

  o  Several help files have been updated to describe the 
     corresponding 'plot.' functions.

  o  Several typos have been fixed.


------------------------------------
- Changes in difR 3.2 (2010-10-04) -
------------------------------------

MINOR UPDATES

  o  The reference 'Magis, Beland, Tuerlinckx, and De Boeck (in
     press)' has been updated as the paper is now published. 

  o  Some typos have been fixed. 


------------------------------------
- Changes in difR 3.1 (2010-06-22) -
------------------------------------

MAJOR UPDATES

  o  The variance of the log odds-ratio statistic (Philips and
     Holland, 1987) has been added as output of the 'mantelHaenszel'
     function. 

  o  The 'difMH' method has a new input argument called 'MHstat'. It
     specifies which DIF statistic must be considered. Default value
     'MHChisq' sets the chi-square statistic, while 'logOR' imposes
     the log odds-ratio statistic.

  o  The commands 'print.MH', 'plot.MH', 'selectDif' and 'dichoDif'
     have been updated according to the changes in the 'difMH'
     command.

  o  The 'breslowDay' method has a new input argument called 'BDstat'.
     It specifies which DIF statistic must be considered. Default
     value 'BD' sets the Breslow-Day statistic as recommended by 
     Aguerri et al. (2009), while 'trend' imposes the trend test
     statistic as recommended by Penfield (2003).

  o  The commands 'print.BD', 'selectDif' and 'dichoDif' have been
     updated according to the changes in the 'difBD' command.


MINOR UPDATES

  o  Some typos have been fixed. 

  o  The reference 'Aguerri et al.' in the 'breslowDay' and 'difBD'
     commands has been updated.


------------------------------------
- Changes in difR 3.0 (2010-04-20) -
------------------------------------

MAJOR UPDATES

  o  The Wald statistic can now be used to flag items as DIF with
     both the logistic and the generalized logistic regression
     method. The new argument 'criterion' permits to select between
     'LRT', the usual likelihood-ratio test, and 'Wald' for the
     Wald test. For the latter, an appropriate contrast matrix is
     built up internally.

  o  The command 'subtestLogistic' has been added to identify DIF
     items among a subset of groups of examinees, using the output 
     of the 'difGenLogistic' command and the Wald test. Subtests are
     performed with appropriate contrast matrices built up 
     internally.

  o  The standardized P-DIF statistics can now be computed with
     different weights. The default weights are based on the focal
     group, but other options are weights based on the reference
     group or on both groups together. The newly added argument
     'stdWeight' in the functions 'stdPDIF' and 'difStd'.

  o  A second measure of effect size has been added for the 
     standardization method. It is a Delta measure, similar to 
     that of the Mantel-Haenszel method, and is described in Dorans 
     (1989, p.228, Eqn. 15).


MINOR UPDATES

  o  The DESCRIPTION and CITATION files have been updated. 

  o  The help file references have been updated.

  o  Several typos have been fixed in the help files. 

  o  As a consequence of the first aforementioned major update,
     the first output argument of the 'Logistik' and 'genLogistik'
     functions, previously called 'deviance', have been renamed to
     'stat'.

  o  The functions 'selectDif', 'dichoDif', 'selectGenDif' and
     'genDichoDif' have been updated to incorporate the different
     changes of this version of difR.

  o  The coding of the effect size, which was previously done by
     means of star symbols (*, ** and ***), has been replaced by
     capital letters A, B and C for respectively negligible,
     moderate and large DIF sizes. This is to match the usual
     ETS conventions, and the change was made within the functions
     'difMH', 'difStd', 'difLogistic' and 'difGenLogistic'.

  o  The TODO file has been added as a list of updates or adds-on
     for further versions of difR.

  o  The general 'difR-package' Rd file has been created. It contains
     a summary of the difR package, with a list of the methods
     currently implemented and a list of related references.



------------------------------------
- Changes in difR 2.2 (2010-01-23) -
------------------------------------

MINOR UPDATES

  o  The system files LICENSE and NEWS have been rewritten for an 
     easier display in Rgui. Several non-ASCII characters have also
     been removed.



------------------------------------
- Changes in difR 2.1 (2010-01-13) -
------------------------------------

MINOR UPDATES

  o  The file CITATION has been created and added to the difR package.

  o  The display of the output of Mantel-Haenszel, standardization,
     logistic regression and generalized logistic regression have been
     slightly modified: the codes for the effect sizes are now 
     returned as "Effect size codes" and not "Signif. codes" as in the
     previous version of difR.

  o  Several issues regarding non-ASCII characters in the help files 
     have been fixed.

 

------------------------------------
- Changes in difR 2.0 (2009-12-18) -
------------------------------------

MAJOR UPDATES

  o  The logistic regression method has been improved. In addition to 
     the deviance statistics, the function 'Logistik' also returns the
     fitted parameters of the two nested models which are compared by 
     means of the likelihood-ratio test. Moreover, the argument 'type'
     has been added to test either nonuniform ('type="nudif"'), 
     uniform ('type="udif"') or both DIF effects simultaneously 
     ('type="both"'). The 'difLogistic' function has been updated 
     acordingly, and returns the matrix with the fitted parameters of
     the best model for each item.

  o  The 'plot.Logistic' function has been improved to allow for 
     plotting the logistic curves of any selected item according to
     the best model retained in the 'difLogistic' function.

  o  The 'plot.Lord' function has been improved to allow for plotting
     the item characteristic curves of any selected item, according to
     the model fitted and the returned item parameter estimates by the
     'difLord' function.

  o  The 'plot.GenLord' function has been improved to allow for 
     plotting the item characteristic curves of any selected item, 
     according to the model fitted and the returned item parameter 
     estimates by the 'difGenLord' function.

  o  The generalized logistic regression method is now available. It 
     extends the logistic regression to more than one focal group, by 
     an appropriate extension of the logistic models and the 
     comparison of model parameters. The functions 'genLogistik' and 
     'difGenlogistic' are the corresponding versions of 'Logistik' and
     'difLogistic' for this generalized method. 

  o  Generalized versions of the functions 'selectDif' and 'dichoDif' 
     have been developed for comparing the results of the generalized 
     tests that are currently available (generalized Mantel-Haenszel, 
     generalized Lord's chi-square test and generalized logistic 
     regression). These are the 'genSelectDif' and 'genDichoDif' 
     functions. They operate similarly to their "non-generalized" 
     versions.

  o  Some measures of effect size are now available. For 
     Mantel-Haenszel method, the effect size is the estimated common 
     odds ratio, up to a transformation, to get the Delta measure on 
     the ETS delta scale. For the standardization method, the 
     standardized P-DIF statistic is used as the measure of effect 
     size and the classification proposed by Dorans, Schmitt and 
     Bleistein (1992) is adopted. For logistic regression and 
     generalized logistic regression, the effect size is the 
     difference in nagelkerke's R^2 coefficients between the two 
     tested models. Both classification scales of Zumbo and Thomas 
     (1997) and Jodoign and Gierl (2001) are available. These measures
     of effect sizes are displayed by the 'print' functions of the 
     different methods. 
    

MINOR UPDATES

  o  The functions 'selectDif' and 'dichoDif' have been updated to fix
     a minor bug occuring when Lord or Raju method was requested: the
     arguments 'engine', 'irtParam' and 'same.scale' were not passed
     correctly to thes functions.

  o  The examples taking a long time to run have been fixed using the
     'Not run' approach.

  o  A minor bug was fixed in the Examples section of the 
     'mantelhaenszel' function: the definition of the data and group 
     variable were incorrect.

  o  The significance code for standardization method was corrected 
     in the 'difStd' function.

  o  The description of the package (in file DESCRIPTION) has been 
     slightly modified.

  o  The help files of the commands 'breslowDay' and 'difBD' have been
     updated to mention that the currently implemented Breslow-Day 
     statistic is the one given by Aguerri et al. (in press) and NOT 
     the statistic for the test of trend in odds ratio heterogeneity 
    (Penfield, 2003).



------------------------------------
- Changes in difR 1.1 (2009-10-27) -
------------------------------------

MINOR UPDATES

  o  The output of 'itemPar2PL' function was corrected to fix a bug. 
     The parameter estimates of the item difficulties were actually 
     not returned as item difficulties (in the IRT sense) but as 
     additive intercept parameters as described in the help file of 
     the 'ltm' function of the eponymous package. Version 1.1 of 
     difR was corrected to return the correct item difficulty 
     estimates. Note that functions 'itemPar1PL', 'itemPar3PL' and 
     'itemPar3PLconst' were not affected by this bug.

  o  The listing of the authors was corrected in the reference manual
     to fix a printing mistake.

  o  Several R codes in the Example sections have been preceded by the
     '#' symbol, so that they are not executed when copy-pasting the 
     full R code from these sections. However, the R code itself 
     remains functioning but it was not executed during the building 
     of the difR package version 1.1. Anyone interested in seeing how
     the command works has just to copy-paste the R code without the 
     '#' symbol. This is mentioned in the help files by the 
     '(remove #)' message.