EFFICIENT ESTIMATION OF FACTOR MODELS
提出广义主成分估计量（GPCE）来估计因子模型中的因子和因子载荷空间，证明其渐近分布，并显示其方差小于传统主成分估计量，从而提高预测效率。
This paper considers the factor model X t = Λ F t + e t . Assuming a normal distribution for the idiosyncratic error e t conditional on the factors { F t }, conditional maximum likelihood estimators of the factor and factor-loading spaces are derived. These estimators are called generalized principal component estimators (GPCEs) without the normality assumption. This paper derives asymptotic distributions of the GPCEs of the factor and factor-loading spaces. It is shown that variance of the GPCE of the common component is smaller than that of the principal component estimator studied in Bai (2003, Econometrica 71, 135–172). The approximate variance of the forecasting error using the GPCE-based factor estimates is derived and shown to be smaller than that based on the principal component estimator. The feasible GPCE (FGPCE) of the factor space is shown to be asymptotically equivalent to the GPCE. The GPCE and FGPCE are shown to be more efficient than the principal component estimator in finite samples.