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

	* robust 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

Changes since version 0-3.2
	
	* a lot of typos of the man pages have been fixed

	* functions pcdtest, pcdres have been added.

	* for hausman taylor model, the summary now prints the variables
	and not the effects

	* the estimation of a model with only one explanatory variable
	using plm with method = "fd" is now working correctly

Changes since version 1-0.0

	* lag and diff methods for pseries are now exported and therefore
	behave correctly

	* for two-ways within models with instrumental variables, K is
	replaced by K+1 for the computation of the overall mean matrix of
	the instruments. Time fixef are now computed. The error message
	"impossible ..." is removed
	
	* a bug in the time random effect model is corrected
	
	* a model.matrix method for panelmodel is provided
	
	* models without intercept (-1 in the formula) should now be
	consistently estimated with plm, pggls and pvcm.
	
	* plm depends now on the Formula package which provides
	useful tools for formula with two parts


Changes since version 1-0.1
	
	* the plm function has been completely rewriten,

	* the names of some arguments have changed (random.methods ->
	ercomp, inst.method -> ivar), the old names are accepted with a
	warning,

	* the model argument of plm objects are now ordinary data.frame,
	and not data.frame with elements y and X. Moreover, this
	data.frame contains untransformed data

	* the data sets which are relevant for panel data estimation that
	where previously in the Ecdat package are now in the plm package

	* in pvcm a bug when the estimation was made on a subset is fixed

	* ercomp is a stand alone function which returns the estimation of
	the components of the variance of the errors,
	
	* the estimation of two-ways within model is now implemented for
	unbalanced panels,

	* the fixef method is much improved, the fixed effects may be
	computed in levels, in deviation from the first level or in
	deviation from the overall mean
	

	
