Before revision:  It is found that the limiting distribution of the estimated instrument effect has a discontinuity when the strength of the idiosyncratic beta is near zero , which makes usual inferences fail to be valid and produce misleading results.
After revision:  It is found that the limiting distribution of the estimated instrument effect has a discontinuity when the variance of the idiosyncratic beta is near zero , which makes usual inferences fail to be valid and produce misleading results.