diff --git a/R/covariance.GMM.R b/R/covariance.GMM.R
index 6c5b67a..e0cf340 100644
--- a/R/covariance.GMM.R
+++ b/R/covariance.GMM.R
@@ -8,12 +8,12 @@
 #' Estimated covariance matrix
 #' @param conditions.vector Vector of moment conditions
 #' @param param Vector of estimated parameters
-#' @param sample Individual data sample
+#' @param data Individual data sample
 #' @param ... Functions of the vector of moment conditions
 #' @return A square covariance matrix
 #' @export covariance.GMM
 #' @author François Pelletier
-covariance.GMM <- function(conditions.vector,param,sample...)
+covariance.GMM <- function(conditions.vector,param,data,...)
 {
-	t(conditions.vector(param,sample,...)) %*% conditions.vector(param,sample,...) / length(sample)
+	t(conditions.vector(param,data,...)) %*% conditions.vector(param,data,...) / length(data)
 }
\ No newline at end of file
diff --git a/R/iterative.GMM.R b/R/iterative.GMM.R
index 8774529..63dc27b 100644
--- a/R/iterative.GMM.R
+++ b/R/iterative.GMM.R
@@ -7,7 +7,7 @@
 
 #' Iterative GMM method
 #' 
-#' @param start Starting values for the parameters and lagrangian
+#' @param start.value Starting values for the parameters and lagrangian
 #' @param conditions.vector Vector of moment conditions
 #' @param data Individual data sample
 #' @param W Weighting matrix
@@ -17,14 +17,14 @@
 #' @return A list containing the optimized vector of parameter and corresponding covariance matrix
 #' @export iterative.GMM
 #' @author François Pelletier
-iterative.GMM <- function(start,conditions.vector,data,W,...,max.iter=50,epsilon=1E-6)
+iterative.GMM <- function(start.value,conditions.vector,data,W,...,max.iter=50,epsilon=1E-6)
 {
-	theta1 <- optim.GMM(start,conditions.vector,data,W,...)
+	theta1 <- optim.GMM(start.value,conditions.vector=conditions.vector,data=data,W=W,...)$par
 	i <- 1
 	repeat
 	{
-		theta2 <- optim.GMM(theta1,conditions.vector,data,W,...)
-		S <- covariance.GMM(conditions.vector,param,data,...)
+		theta2 <- optim.GMM(theta1,conditions.vector,data,W,...)$par
+		S <- covariance.GMM(conditions.vector,theta2,data,...)
 		if(sqrt(sum((theta1-theta2)^2))<epsilon)
 			return(list(par=theta2,cov=S))
 		else if (i>max.iter)
diff --git a/R/optim.GMM.R b/R/optim.GMM.R
index af8c28a..4a03b35 100644
--- a/R/optim.GMM.R
+++ b/R/optim.GMM.R
@@ -7,7 +7,7 @@
 
 #' Optimization for GMM method
 #'
-#' @param start Starting values for the parameters
+#' @param start.value Starting values for the parameters
 #' @param conditions.vector Vector of moment conditions
 #' @param data Individual data sample
 #' @param W Weighting matrix
@@ -15,7 +15,7 @@
 #' @return a list with optimization results
 #' @export optim.GMM
 #' @author François Pelletier
-optim.GMM <- function(start,conditions.vector,data,W,...)
+optim.GMM <- function(start.value,conditions.vector,data,W,...)
 {
-	optim(start,objective.GMM,conditions.vector,data,W,...)
+	optim(start.value,objective.GMM,gr=NULL,conditions.vector,data,W,...)
 }
\ No newline at end of file
diff --git a/man/covariance.GMM.Rd b/man/covariance.GMM.Rd
index 9b0e6dd..38da47d 100644
--- a/man/covariance.GMM.Rd
+++ b/man/covariance.GMM.Rd
@@ -2,14 +2,14 @@
 \alias{covariance.GMM}
 \title{Estimated covariance matrix}
 \usage{
-covariance.GMM(conditions.vector, param, sample...)
+covariance.GMM(conditions.vector, param, data, ...)
 }
 \arguments{
   \item{conditions.vector}{Vector of moment conditions}
 
   \item{param}{Vector of estimated parameters}
 
-  \item{sample}{Individual data sample}
+  \item{data}{Individual data sample}
 
   \item{...}{Functions of the vector of moment conditions}
 }
diff --git a/man/iterative.GMM.Rd b/man/iterative.GMM.Rd
index 106facb..71e6a39 100644
--- a/man/iterative.GMM.Rd
+++ b/man/iterative.GMM.Rd
@@ -2,11 +2,11 @@
 \alias{iterative.GMM}
 \title{Iterative GMM method}
 \usage{
-iterative.GMM(start, conditions.vector, data, W, ..., max.iter = 50,
+iterative.GMM(start.value, conditions.vector, data, W, ..., max.iter = 50,
   epsilon = 1e-06)
 }
 \arguments{
-  \item{start}{Starting values for the parameters and
+  \item{start.value}{Starting values for the parameters and
   lagrangian}
 
   \item{conditions.vector}{Vector of moment conditions}
diff --git a/man/optim.GMM.Rd b/man/optim.GMM.Rd
index dd5ddbf..55a46b8 100644
--- a/man/optim.GMM.Rd
+++ b/man/optim.GMM.Rd
@@ -2,10 +2,10 @@
 \alias{optim.GMM}
 \title{Optimization for GMM method}
 \usage{
-optim.GMM(start, conditions.vector, data, W, ...)
+optim.GMM(start.value, conditions.vector, data, W, ...)
 }
 \arguments{
-  \item{start}{Starting values for the parameters}
+  \item{start.value}{Starting values for the parameters}
 
   \item{conditions.vector}{Vector of moment conditions}