A covariate is a factor that you cannot directly control, but that you can measure. When these measurements on the experimental units that are intended for an experiment are available, it is useful to include these variables as design factors.
The Custom Design platform constructs a design that selects covariate values in an optimal fashion. Covariate values are selected from an existing data table that provides covariate information about the potential experimental units. You can specify a number of runs that is smaller than the number of experimental units listed in your data table. You can also specify covariates that are hard-to-change. When you make your design and the design has fewer runs than the number of rows in the covariate table, the design table includes a Covariate Row Index column.This column indicates the row from the covariate table that corresponds to each experimental run.
Note: The number of rows in the covariate data table where covariate factors have nonmissing values must be greater than or equal to the specified Number of Runs.
The following examples illustrate constructing designs with covariates using the Custom Design platform.
• Design with Fixed Covariates