Changes since version 0-1.2
* Models with only one explanatory variable resulted in a bug. This has been fixed.
* Estimation methods are now available with four functions : plm, pvcm, pggls and pgmm instead of one (plm) in the previous version.
* pvcm is a new function which estimate variable coefficients models. The "nopool" model is now part of it.
* pggls is a new function which enables the estimation of general FGLS.
* pgmm is a new function for general method of moments estimator.
* for all estimation functions, the four first arguments are now formula,data,effect,model
* robus inference is now provided by the pvcovHC function.

Changes since version 0-2.1
* pdata.frame is much faster thanks to a modification of the pvar function
* series with only NA values or with constants values are now removed by pdata.frame
* observations are ordered by id and time by pdata.frame
* a pfix function is added to edit a pdata.frame
* a as.data.frame function is provided to coerce a pdata.frame to a data.frame
* the dependency to the Matrix package has been removed and pgmm is much faster now
* phtest has been fixed to return only positive values of the statistic
* pgmm objects now inherits from panelmodel like other estimators and prints correctly
* a bug in summary.pgmm has been fixed

Changes since version 0-2.2
* the coefficients method for objects of class pgmm is now exported.
* a bug in the plm method of plmtest has been fixed
* in plmtest, the argument effect "id" is renamed "individual"
* three testing functions are added : pbsytest (Bera, Sosa-Escudero and Yoon test), pARtest (Breush Godfrey Test) and pDWtest (Durbin-Watson test), pwartest, pBGtest, pwtest pbltest 
* plm, pvcm and pggls now have arguments "subset" and "na.action"
* phtest, pFtest, plmtest now have a formula method
* a bug is fixed for the vcov of the within model
* the pdata.frame function and class is suppressed. The package now use ordinary data.frames. 

Changes since version 0-3.1
* in plm.formula, [int.row.names] is replaced by [as.character(int.row.names)]
* the degree of freedom for a within time effect model was wrong and has been corrected.
* the arguments type and weights in pvcovHC.panelmodel are renamed method and type respectively. The default method (type in previous versions) is arellano and not white1
* honda is now the default option for plmtest