Citations:required


 * 1) * 1934, A. C. Aitken, "Note on Selection from a Multivariate Normal Population", Proceedings of the Edinburgh Mathematical Society 4, page 106:
 * From a population characterised by variables $$x,\ y,\ z$$, a sub-population is extracted by selection in $$x$$ alone. It is required to determine the new values, in the selected population, of the means and variances of $$y$$ and $$z$$.