Do these folks study speech and know what to control for at all? Seems there are more critical confounding factors a study is likely to observe before psycho-ac

Do these folks study speech and know what to control for at all? Seems there are more critical confounding factors a study is likely to observe before psycho-active drug use is a significant factor https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2790192/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2790192/