如果选择first，窗口中就会直接显示first-stage的regression output；如果选择ffirst，则会显示first-stage中检测IV的相关性等的test statistics。

谢谢，请问2SLS中xtivreg2和xtivreg的结果应该一样吗？不管是系数还是p值。谢谢

应该是的。xtivreg2的功能更强大些：Its features include:  two-step feasible GMM estimation (gmm2s option) and continuously-updated
GMM estimation (cue option); LIML and k-class estimation; automatic output of overidentification and underidentification test statistics; C statistic test
of exogeneity of subsets of instruments (orthog() option); endogeneity tests of endogenous regressors (endog() option); test of instrument redundancy
(redundant() option); kernel-based autocorrelation-consistent (AC) and heteroskedastic and autocorrelation consistent (HAC) standard errors and covariance
estimation (bw(#) option), with user-specified choice of kernel (kernel() option); two-level cluster-robust standard errors and statistics; default
reporting of large-sample statistics (z and chi-squared rather than t and F); small option to report small-sample statistics; first-stage regressions
reported with various tests and statistics for identification and instrument relevance; ffirst option to report only these identification statistics and
not the first-stage regression results themselves.  ivreg2 can also be used for ordinary least squares (OLS) estimation using the same command syntax as
official regress and newey.
摘自-help xtivreg2-

谢谢哈

学习了