Zach is measuring nonverbal behavior and personality traits to see if certain personality types display more nonverbal behaviors. However, Zach is having an issue deciding how he will actually record nonverbal behaviors in the lab. He wants to measure facial expressions only, but then also considers using body language and vocalics instead. This process of deciding how to measure a variable of interest is known as what?

Operationalization

Explanation:

In study design, particularly in neuroscience, operationalization refers to the process of determining the estimation of a behavior which is not clearly observable while certain phenomena indicate its presence. Therefore operationalization describes a fuzzy definition such that empirical study makes it easily distinctive, observable, and understandable.

Thus, from the above we can conclude that the given case illustrates operationalization.