Oscar Kempthorne2014-06-172014-06-171956-09Reprinted from The Annals of Mathematical Statistics, Vol. 27, No. 3, September, 1956http://hdl.handle.net/123456789/2984It is shown that the efficiency factor of a design is r times the harmonic mean of the latent roots of the reduced intrablock normal equations exclusing the root which is always zero.enArticle