Definitions for "Covariates"
Covariates are extraneous variables that might have an impact on the experimental results. For example, the income or age of the respondent, the time of day, or a telephone rep's rating on selling skills, might be expected to impact the results of some multivariate tests. Such variables are not under the control of the experimenter, but can be "adjusted" by measuring them and then including them in a covariate analysis. Optimal Designs permit the addition of a few additional combinations to allow for this adjustment.
A set of explanatory variables.