[mrighele]

I think that's because it depends not only how much you drink, but also how often.

For example if you drink 4 beers in one night, you may consider that night as heavy drinking, but you are not heavy drinking in general if you do it once every month or two. You're more of a drinker if you get a glass of wine every night while reading your book.

[soco]

While it would make sense, I don't think I've seen this distinction either in comments or in studies. They talk about the same amount daily whatever that is.