On the multiple correlation of brothers, being a note on Mr J. O. Irwin's memoir, and on my statement of the application of Galton's difference problem to the determination of the degree of relationship of brothers, made in August 1902
Pearson, Karl, On the multiple correlation of brothers, being a note on Mr J. O. Irwin's memoir, and on my statement of the application of Galton's difference problem to the determination of the degree of relationship of brothers, made in August 1902, Biometrika , 17(1/2), 1925, pp. 129-141