Another look at ANCOVA versus blocking.

Compared methods of incorporating a concomitant variable into an experimental design. A 3?×?3 conceptual framework for these methods was developed, with one dimension representing 3 methods of assignment to treatment groups and the other dimension representing 3 methods of data analysis. Monte Carlo procedures were used to investigate the relative statistical power and apparent imprecision of the 9 methods. Results show that the recommendation of most experimental design texts to consider the correlation between the dependent and concomitant variables in choosing the best technique for utilizing a concomitant variable is incorrect. Instead, the 2 factors that should be considered are whether scores on the concomitant variable are available for all Ss prior to assigning any Ss to treatment conditions and whether the relationship of the dependent and concomitant variables is linear. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)