Define a covariate

[#1]

My understanding is this:

• A factor is categorical variable
• A covariate is a continuous variable

Why do JMP define and use covariate differently?

What is  the correct definition of a covariate?

[#2]

In experimentation, you have two types of variables.  The ones you are willing to control (e.g., design factors) and the ones you are not (e.g., noise).  A covariate is one way to handle measurable noise.  There are other ways to handle noise in an experiment (e.g., RCBD, BIB, repeats, replicates, split-plots).