“…Now, let us make the extreme simplification, as in our empirical section, thatx = [1 0 K ], so that firm characteristics have zero sample mean -apart for the first one. This is not uncommon in the recent literature as long as the data is preprocessed (see Freyberger et al (2020), Gu et al (2020b), Kelly et al (2019) and Koijen and Yogo (2019)). Then, X X = N diag(σ 2 X ), where the modified vector of variancesσ 2 X is simply σ 2 X with the first element equal to one (instead of zero).…”