"Drunk people were seen as more extroverted - they were more gregarious, assertive, and participated in the conversation more", says Winograd.
After a 15-minute absorption period, volunteers worked through a series of group activities - including discussion questions and logic puzzles - meant to elicit a variety of personality traits and behaviours.
Instead, scientists believe this difference might come down to inherent differences in point of view. The level of alcohol consumed in the most recent study was enough to be too drunk to drive but probably doesn't capture the full extent of a personality changes after a night of heavy drinking.
Winograd offers an explanation for how both the external observers and the participants in the most recent study could both be right, even if they came to different conclusions about how much personality changed. Two weeks before, they used a 50-item questionnaire so the subjects can self-report their usual sober and drunk personality traits.
"Participants reported experiencing differences in all factors of the Five Factor Model of personality, but extraversion was the only factor robustly perceived to be different across participants in alcohol and sober conditions", said Winograd.
Participants were broken into groups and given either non-alcoholic drinks or beverages tailored to produce about a.09 blood alcohol content.
Over the next 15 minutes, they were given beverages to drink - some participants received soft drinks, while others were given vodka-soda cocktails created to produce a blood alcohol content of around.09. They were also asked to describe their own "drunk personality" throughout the experiment.
Once breathalyzed, the participants were given group activities such as puzzles and discussion questions, during which they displayed their personalities. Video recordings of their activity were supplied to outside observers who filled in standardized assessments of each individual's personality traits.
More and more research indicates that for many of us, alcohol doesn't transform personality overall, though it does tend to make people more extroverted. They also reported higher levels of extraversion and emotional stability, but those observing only noticed changes in one trait - the extraversion.
The study, which is being reported around the world, required many students to suffer hangovers in the pursuit of science and was carried out at the U.S. University of Missouri.
The researchers said this makes sense considering extraversion is the most outwardly visible personality factor.
Researchers have yet to test their findings outside the lab in a social setting such as a bar or party.
"Most importantly, we need to see how this work is most relevant in the clinical realm and can be effectively included in interventions to help reduce any negative impact of alcohol on peoples' lives", concludes Winograd.