I have had this issue come up a few times in doing a DOE where I have a set of units where each one can be reused in testing, but it is a specific set with specific settings that I want to model the impact of.

So, for example, I may have 12 units where 4 are from Category A, 3 are from Category B, and 5 are from Category C (shown in the table below). I am going to be testing with this category as a categorical factor, along with two continuous factors (temperature and humidity). But I can perform however many tests are needed. I'm interested in interaction effects and in second order effects. Is there a way to have a table set up with the units available and then re-use the units within the DOE platform? Whenever I try to use Add Factor >> Covariate, I am limited to at a max, the number of rows in the covariate table and cannot reuse units.

**Unit ID** | **Category** |
---|

1 | A |

2 | A |

3 | A |

4 | A |

5 | B |

6 | B |

7 | B |

8 | C |

9 | C |

10 | C |

11 | C |

12 | C |