Theoretical framework

Hi,

I would like to know when we want to include relevant theory in the literature review section,
the theory is that necessary to be directly mentioned about the relationship between XX and XX?

For example, can I include agency cost theory in order to indicate that there is a negative relationship between leverage and dividend policy. This is because debt and dividend are the alternative mechanisms in monitoring the managers and controlling agency-related problems. Although the theory’s author himself did not mention about it, but many prior empirical studies infer this relationship based on agency cost theory.

OR
I have to include theory that the theory’s author himself specifiy the relationship btw the variables in his theory such as using dividend relevance theory to show the relationship between dividend policy and shareholders wealth?

Thanks