AY1214=merge(x=AY12,y=AY14,by.x=c("nquest","nord"),by.y=c("nquest","nordp"))
AY1214=subset(AY1214,select=c("ylm.x","STUDIO","STACIV","ETA.x","SEX","ylm.y","studio","staciv","ETA.y","sex"))
panelID=seq(1:nrow(AY1214))
AY1214=cbind(panelID,AY1214)
AY1214=na.omit(AY1214)
D1=AY1214[,c(1,2:6)]
D2=AY1214[,c(1,7:11)]
names(D1)=names(D2)=c("panelID","ylm","studio","staciv","eta","sex")
D=rbind(D1,D2)
D=D[sort.list(D$panelID),]

head(D)

ybar=tapply(D$ylm,INDEX=D$panelID,FUN=mean)
ybar=rep(ybar,each=2)
xbar=tapply(D$eta,INDEX=D$panelID,FUN=mean)
xbar=rep(xbar,each=2)
xtilde=D$eta-xbar
ytilde=D$ylm-ybar

beta=sum(xtilde*ytilde)/(sum(xtilde*xtilde))

ybar=tapply(D$ylm,INDEX=D$panelID,FUN=mean)
xbar=tapply(D$eta,INDEX=D$panelID,FUN=mean)
a=ybar-xbar*beta



PD=plm.data(D,index="panelID")
pm=plm(ylm~eta,data=PD,model=c("within"),effects="individual")

pm=plm(ylm~eta,data=PD,model=c("random"),effects="individual")



summary(pm)