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


-----------------------------------
- Changes in diR 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 diR 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 diR 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 diR 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.