1. On least squares and linear combination of observations;Aitken;Proc. Royal Soc. Edinburgh A,1934
2. G. Alpargu, G.P.H. Styan, A third bibliography on the Frucht–Kantorovich Inequality and on some related inequalities, in: S. Jensen, G.P.H. Styan (Eds.), The Seventh International Workshop on Matrices and Statistics, Ft. Lauderdale, December 11–14, 1998, McGill University, Montreal, pp. 17–26
3. The inefficiency of least squares;Bloomfield;Biometrika,1975
4. The geometry of estimation;Durbin;Biometrika,1951
5. C.F. Gauss (1821). See J. Bertrand (1888) Calcul des probabilités, or A. Borsh, P. Simon Abhandlangen zur Methode der kleinsten Quadratic von Carl Friedrich Gauss, Würzburg, 1887