Assuming caffeine/cup is linear (2 cups =~ 2x caffeine), the second graph you made shows caffeine consumption vesus age. Since average consumption goes down in

Assuming caffeine/cup is linear (2 cups =~ 2x caffeine), the second graph you made shows caffeine consumption vesus age. Since average consumption goes down in the last age group, your sample does not show a steady increase with age. edit: Think of it as an increase in the 7+ category being counterbalanced by a bigger drop in the lower categories.