F-statistic is below Stock and Yogo's critical values. However, R squared and Shea's partial R squared are not low. There is no serial autocorrelation problem. The disturbance is homoskedastic. Sargan, Hansen and C-statistic show an instrumental variable is exogenous to the error term thus satisfies the exogeneity condition. The only problem is the instrument is weak in the relevance test although it is relevant to the endogenous variable (its first-stage regression coefficient is significant at 0.001 level.