From a paper of Gao, Whited, and Zhang (2021), I saw a paparagraph
We deviate from this traditional specification in three ways: we examine only money held by corporations, we include real GDP growth in the regression to control for economic fluctuations over the business cycle, and we use real instead of nominal interest rates. This last choice is for internal consistency with the theoretical framework that follows
I understand the internal consistency from this description
For example, if a respondent expressed agreement with the statements "I like to ride bicycles" and "I've enjoyed riding bicycles in the past", and disagreement with the statement "I hate bicycles", this would be indicative of good internal consistency of the test.
But I am wondering when we should use "internal consistency" and why the authors need to perform the robustness test for it afterwards?