Thread: bracketing and matrixing

Can anybody translate to me the meaning of this two words in this context. Thanks in advance

"This document provides guidance on bracketing and matrixing study designs. Specific principles are defined in this guideline for situations in which bracketing or matrixing can be applied. Sample designs are provided for illustrative purposes, and should not be considered the only, or the most appropriate, designs in all cases".

Hi Fernando!
Is this paragraph refering to graphic design, or which kind?

It is about a guideline for stability studies for pharmaceutical products. But dont´t worry. I believe that I understood the sense of the expression, it´s pretty technical.
Thank you anyhow