I believe the standard cup of coffee is defined as 8oz/250ml. With interview studies like that it’s harder to get exact measurements so they have big error bars and rely on having a standard reply to show the person how big a cup is.
Technically, what they end up concluding is that people who drink an amount of coffee they would describe to someone with a clipboard as 2-3 cups are less anxious. I’m willing to bet there’s a good correlation between between that and drinking between 400 and 750 mL of coffee a day as well. :P







Totally. I think some of the issue is “coffee cup” vs “cup of coffee”, with one being the volume of the mug and the other being the amount of coffee in said mug.
With the medical advice, I think it kinda deliberately vague, since you can’t be that precise at home and they don’t know the number that precisely to begin with.