Factorial 2^{<i>p</i>–<i>q</i>}Plans Robust Against Linear and Quadratic Trends

Abstract

When the substrate of a 2 n–q factorial or fractional factorial experiment may be expected to show trends representable by linear and quadratic terms in time, then certain orderings spaced at equal time-intervals permit better estimation of the effects than do others. Some of these ordered plans are given for p – q = 2, 3, 4, 5. Simple methods are given for computing effects, trends, and efficiencies.