“…In this respect, some of the most widely used economic theories both theoretically and empirically are based on factor models (e.g., the ATP of Ross, 1976). The multifactor models have been widely employed and examined in finance and portfolio theory, including by Ross (1976), Fama and French (1993), Bai (2003), Ait-Sahalia and Xiu (2017), Bollerslev, Meddahi, and Nyawa (2019), Ortobelli et al (2019), and the references therein. When the factors are latent, principal component analysis (PCA) obviously becomes the key tool to the decision maker (Ait-Sahalia & Xiu, 2017;Jolliffe, 2002).…”