The UCL Research Department of Epidemiology and Public Health in London carried out a study to measure actual and perceived amounts of alcohol in a self-defined usual glass of wines and spirits in the general population.
Participants were a convenience sample of adults who drink alcohol or who pour drinks for other people (n = 283, 54% women) at 6 sites in South East England. The survey was face to face and comprised a self-completion questionnaire and pouring task. Estimation accuracy, categorised as correct (±0.5 units), underestimate (>0.5 units), or overestimate (>0.5 units) was the main outcome.
The mean number of units poured was 1.90 (SD 0.80; n = 264) for wine and 1.93 (SD 0.78; n = 201) for spirits. The amount of alcohol in a self-defined usual glass was estimated in 440 glasses (248 wine and 192 spirits). Overestimation took place in 42% glasses of spirit poured and 29% glasses of wine poured, and underestimation in 17 and 19%, respectively. Regression analysis found that the volume poured was significantly associated with underestimating both wines and spirits, and additionally for wine only, belonging to a non-white ethnic group and being unemployed or retired. Not having a university degree was significantly associated with overestimating both drink types.
Source: Actual and Perceived Units of Alcohol in a Self-Defined “Usual Glass” of Alcoholic Drinks in England. Boniface S, Kneale J, Shelton N. Alcohol Clin Exp Res. 2012 Dec 20.