One omitted hard part is to accurately determine caffeine content which can fluctuate widely depending on the beans, roasting, brewing method, water temperature

One omitted hard part is to accurately determine caffeine content which can fluctuate widely depending on the beans, roasting, brewing method, water temperature ... E.g. 100% robusta coffee can be nearly double in caffeine than 100% arabica coffee.[0] Another important thing also missing in this context is the individual "activity" of the CYP1A2 enzyme which helps to metabolize caffeine (so called "fast" or "slow metabolizer"); it is dependent on genetics and environmental factors. [1] E.g. a regular smoker breaks down caffeine a lot faster. [0]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8228209/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8228209/ [1]https://pubmed.ncbi.nlm.nih.gov/33397254/ https://pubmed.ncbi.nlm.nih.gov/33397254/