FWL theorem

In econometrics, the FWL theorem (Frisch-Waugh-Lovell theorem) is named after the econometricians Ragnar Anton Kittil Frisch, F. Waugh, and M. Lovell.

The theorem states that the determination of the coefficients in a standard regression model via ordinary least squares and a method involving projection matrices are equivalent.

Literature
Econometrica, Vol. 1, No. 4. (Oct., 1933), pp. 387-401.
 * Ragnar Frisch; Frederick V. Waugh "Partial Time Regressions as Compared with Individual Trends"


 * Lovell, M., 1963, Seasonal adjustment of economic time series, Journal of the American Statistical Association, 58, 993-1010.

Teorema di Frisch-Waugh-Lovell