chi2(4) = (b-B)'[(V_b-V_B)^(-1)](b-B)
                          =  -198.36    chi2<0 ==> model fitted on these
                                        data fails to meet the asymptotic
                                        assumptions of the Hausman test;
                                        see suest for a generalized test

请问hausman 检验为负值怎么处理啊！！大侠们求救！！