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Half full or empty: Cues that lead wine drinkers to unintentionally overpour

Walker, Doug, Laura Smarandescu, & Brian Wansink (2014). Half full or empty: Cues that lead wine drinkers to unintentionally overpour. Substance Use & Misuse, 49(3), 295-302. doi:10.3109/10826084.2013.832327.

Increasing awareness about visual illusions and environmental cues can help those who drink alcohol to avoid drinking more than intended. Previous research found that a large number of people do not know what constitutes a standard serving of alcohol. Pouring biases are naturally larger in environments such as at dinner or social gatherings where drink sizes are not regulated as they would be in a restaurant or bar. We conducted research to study what cues and illusions increase the risk of over-pouring wine in a social setting. 

Based on previous research, we hypothesized that, on average, individuals would pour more wine into larger and wider glasses; individuals would pour more wine when a place setting is present, individuals would pour more wine into a glass that they are holding (versus one placed on a table) and that individuals would pour more wine into a glass with low contrast with respect to the color of the wine (ie. white wine in a clear glass).

To test these hypotheses we recruited 73 students and staff (average of 29.1 years) at a northeastern university who reported drinking at least one glass of wine in a given week. Participants were directed to pour a serving of wine based on how much they normally pour for themselves and instructed to repeat this activity at seven “pouring stations” where all aspects were the same except the variable(s) being observed. 504 pours were completed. Each station was equipped with a scale that measured the weight of the empty and filled glass. After individuals completed all seven pours they were asked to complete a questionnaire that asked to what extent (on a nine point scale) various conditions, including those being tested, affect how much wine they pour.

The pour sizes for each of the tested variables show that the glass width, pouring position, and glass color are all significant indicators of over-pouring. On average 11.9% more wine was poured into a wide wine glass versus a standard glass. Individuals also pour 12.2% more when holding the glass versus setting it on the table. When pouring into a clear glass individuals poured 9.2% more white wine than red wine. The size of the glass and whether or not a place setting is present proved to not have a significant effect on how much wine is poured. The results suggest that there is  a relationship between retrospective awareness of bias and over-pouring. Factors that individuals rated as having the greatest impact on how much they poured were, in general, the same factors that actually resulted in over-pouring. In order to avoid unknowingly pouring more than intended, and potentially drinking too much, researchers recommend drinking from narrow glasses that contrast with the color of the wine and setting your glass on the table before pouring.