Describe/define your (possible) variables of interest in your proposal. (My topic is about the ongoing labor shortage that is affecting the United States) [see the attached paper you wrote]

You can include conceptual definitions as well as operational definitions.

Please refer to the lecture of variables before the discussion.

https://support.minitab.com/en-us/minitab-express/1/help-and-how-to/modeling-statistics/regression/supporting-topics/basics/what-are-categorical-discrete-and-continuous-variables/

https://www.statisticssolutions.com/understanding-the-differences-between-constructs-variables-and-operational-definitions/

https://conjointly.com/kb/understanding-variables/

This requires no sources.