Liebe Gloria, the error says it all: you have a singular covariance matrix (the vcov(q) term in the Hausman test); this is not invertible and therefore the test fails.
As for the reasons, this might be either a bug or perhaps an ill-conditioned problem: it is impossible for me to tell without a reproducible example. I can only suggest an alternative strategy (which you must tailor to your example). Another (computationally more robust) way to perform a Hausman test is through an auxiliary regression (see Wooldridge, "Econometric analysis of cross-section and panel data", 10.7.3) #### Hausman test by auxiliary regression ######## library(plm) ## standard Munnell example data(Produc) fm<-log(gsp)~log(pcap)+log(pc)+log(emp)+unemp re<-plm(fm, data=Produc, model="random") fe<-plm(fm, data=Produc, model="within") ## extract transformed data y.re<-pmodel.response(re) X.re<-model.matrix(re) X.fe<-model.matrix(fe) ## check coefficients coef(re) lm(y.re~X.re-1) coef(fe) lm(pmodel.response(fe)~X.fe-1) ## make aux dataset auxdata<-data.frame(cbind(y.re,X.re,X.fe)) colnames(auxdata)<-c("y", paste("x", 1:9, sep="")) ## auxiliary model auxmod<-lm(y~x1+x2+x3+x4+x5+x6+x7+x8+x9-1, auxdata) ## regression-based Hausman test is exclusion test for 6-9 library(lmtest) waldtest(auxmod, 6:9) I will eventually add a production version of this to 'plm' as phtest2(). Best wishes nach Koeln Giovanni Giovanni Millo, PhD Research Dept., Assicurazioni Generali SpA Via Machiavelli 4, 34132 Trieste (Italy) tel. +39 040 671184 fax +39 040 671160 -------- original message ---------------------- Date: Mon, 29 Oct 2012 13:14:09 -0700 (PDT) From: gloria <gbus...@smail.uni-koeln.de> To: r-help@r-project.org Subject: [R] Hausman test error solve Message-ID: <1351541649650-4647793.p...@n4.nabble.com> Content-Type: text/plain; charset=UTF-8 Hello, I am trying to conduct a Hausman test to choose between FE estimators and RE estimators. When I try to run: library(plm) fixed <- plm(ROS ~ DiffClosenessC +ZZiele + AggSK + nRedundantStrecken + Degree + KantenGew + BetweennessC + SitzKappazitaet, data=Panel,index=c("id","time"),model="within") summary(fixed) fixef(fixed) random <-plm(ROS ~ DiffClosenessC +ZZiele + AggSK + nRedundantStrecken + Degree + KantenGew + BetweennessC + SitzKappazitaet, data=Panel,index=c("id","time"), model="random") summary(random) phtest(fixed, random) I get an error from phtest(fixed, random) Fehler in solve.default(dvcov) : System ist f?r den Rechner singul?r: reziproke Konditionszahl = ... Error in solve.default(dvcov) : system is computationally singular: reciprocal condition number =... Can someone Help me with this problem or give me a hint where to look? Thanks gloria -- View this message in context: http://r.789695.n4.nabble.com/Hausman-test-error-solve-tp4647793.html Sent from the R help mailing list archive at Nabble.com. -------------end original message ----------------- Ai sensi del D.Lgs. 196/2003 si precisa che le informazi...{{dropped:12}} ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.