Do studies control for caffeine/coffee usage? Or are most of the conclusions that we draw from studies “true for those who use caffeine”? Most adults consume caffeine and it would be nice to know what the brain thrives on in the absence of any psychoactive compounds.
Unless the study is investigating a hypothesis that is relevant to caffeine/coffee usage, researchers probably won’t control for caffeine/coffee usage.
That said, if caffeine/coffee might significantly affect study outcomes because previous research has demonstrated/suggested that, then researchers may choose to discuss this in the limitations/discussion section.