How much alcohol?

A foaming beer mug. A half-full wine glass. A shot glass of 40-proof liquor.

These are the visual aids used to teach U.S. teenagers about a “standard drink,” each of them representing 14 grams of alcohol. In Austria, however, a standard drink contains 20 grams. In Iceland and the United Kingdom, 8 grams.

Inconsistency among countries in the definitions of a standard drink and of what constitutes low-risk drinking makes it difficult to conduct global research on alcohol use and addiction, say Stanford Medicine researchers. Throw in differences in measurement and terminology — alcohol is not exactly served by the gram — and you have a recipe for confusion among people trying to drink responsibly.

“There’s a substantial chance for misunderstanding,” says Keith Humphreys, PhD, professor of psychiatry and behavioral sciences and senior author of a study that surveyed the definitions of “standard drink” and low-risk drinking in 37 countries. “It is not possible that every country is correct; maybe they are all wrong.” Psychiatric medicine resident Agnes Kalinowski, MD, PhD, is the lead author of the study, which was published in the July 2016 issue of Addiction.