Accuracy of photographs to capture respondent-defined drink size

Evidence suggests that people misjudge the size of their drinks, calling into question the validity of data from surveys and screening instruments assessing alcohol quantity in terms of standard drinks. This article studied the validity of photographs of glasses to assess drink size.

In a U.S. national sample of 323 drinkers, respondents were mailed a measuring beaker and a set of photographs of wine, beer, and other drinking glasses for use in a subsequent telephone survey. In the interview, they were asked to pick the glass most similar to what they use at home and to identify the letter associated with their usual pour level. Then, a protocol where subjects measured the actual number of ounces in their typical drink, by pouring water into their usual glass and measuring this volume using the measuring beaker, gave a direct measure of home drink volume. We compared drink sizes using the two approaches.

Photographs worked well for certain groups, including women, young people, and nonwhites (for wine) and whites (for beer). The greatest magnitude of error arising from the use of photographs was for wine drinks among those age 50 and older, those with a 4-year degree, frequent 5+ drinkers in general, and heavy-volume wine drinkers. Average drink size based on the most popular wine and beer glasses in the photographs were 0.62 oz (18 ml) and 1.62 oz (48 ml) larger than beaker pours, respectively. Error between actual drinks and photographs was especially high for a large balloon-shaped wine glass, chosen by only 3% of wine drinkers.

Whenever possible, researchers and clinicians should incorporate protocols that allow for some type of direct measurement using the actual vessels from home. When this is not viable, photographs represent a solution that is practical, shows promise for beer and wine drinks, and is relevant to any drinking context.