Miscellanea. Some hidden projection properties of orthogonal arrays with strength three
证明了运行次数不是16的倍数的两水平强度三正交阵列具有隐藏投影性质：投影到任意五个因子时，若忽略高阶交互作用，所有主效应和两因子交互作用均可估计。该结果适用于运行次数不是8的倍数的任何强度二正交阵列的折叠反转，扩展了Diamond关于12次运行Plackett-Burman设计折叠反转的结论，并与搜索设计有联系。
It is shown that a two-level orthogonal array with strength three whose run size is not a multiple of 16 has the hidden projection property that in its projection on to any five factors, all the main effects and two-factor interactions are estimable if the hgher-order interactions are neagible. The result applies to the fold-over of any strength-two orthogonal array whose run size is not a multiple of 8. This extends Diamond's (1995) result on the fold-over of the 12-run Plackett-Burman design. Some connections with search designs are also presented.