        **************************************************
        *                                                *
        *  Changes and Developments in the difR Package  *
        *                                                *
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-----------------------------------
- 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 parameteres 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 these
     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 (from 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 
     eponym 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.