ABSTRACT
Blocking is one means of shielding comparisons of interest from unwanted sources of variation. When the experimental units are time (or spatially) ordered and are suspected of producing a trend in the errors, certain run orders provide an alternative means of isolating such variation. Beginning with Daniel and Wilcoxon (Citation1966), statisticians have proposed run orders for 2 k and 2 k − p designs that are robust to linear and quadratic trend. This article discusses the rationale for using such designs and presents an example to illustrate the analysis of trend-robust designs.
ACKNOWLEDGEMENTS
The authors are thankful for a particularly thorough referee who improved the clarity of this article by his very careful reading and numerous suggested improvements.
Notes
Error = 0.004Run2 − 2 + standard Normal; Y = 22 + 2D + E + .75D*E − 0.5H + Error.
PSE = 1.402, based on standardized estimates (= Estimate/Rel. Std. Error).