People are bad at estimating their own blood alcohol concentration, according to scientists

How drunk do you think you are? According to a new study, Queenslanders who’ve had a few are poor estimators of their blood alcohol concentration (BAC).

The study, published in Drug & Alcohol Review, found a notable difference between the BAC that revellers thought they had, and the numbers that actually showed up on a breathalyser.

“We expected to find this result,” says lead author Dr Dominique de Andrade, a research fellow at the Centre for Drug Use, Addictive and Anti-social behaviour Research in Deakin University’s School of Psychology.

The researchers surveyed people in nightclub queues in four Queensland night entertainment precincts: Fortitude Valley and West End in Brisbane, Cairns and Surfers Paradise.

In total, they surveyed 2144 people.

“They were asked if they wanted to partake in a short five-minute survey. A shorter three-minute version of the survey was also developed for those that were short on time or were in queues,” says de Andrade.

Among other things, participants were asked to estimate their BAC, and then used a breathalyser to find the actual amount.

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People with lower BACs were more likely to overestimate the amount of alcohol in their blood,  while those with high BACs were more likely to underestimate it.

“It was interesting that those that were moderately intoxicated (0.05g/dl-0.79g/dl) were most accurate,” says de Andrade.

“We think this is likely due to the public education over the last few decades around legal limits for driving. It also suggests that educating drinkers on blood alcohol concentration and how it relates to standard drinks can be somewhat effective.

“Findings also showed that those that were sober or slightly intoxicated were likely to significantly overestimate which suggests that they may have a poor understanding of the rate that alcohol metabolises in the body.

“Of most concern was the group that underestimated their BAC.”

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Underestimators with a high BAC were also more likely to have been recently ejected from a venue. But the researchers couldn’t find a link between inaccurate BAC estimates and any other experience of harm.

“The relationship between underestimation and forms of harm should be further investigated in future research,” says de Andrade.

While every body responds to alcohol differently, making it hard to draw precise lines between alcohol consumption and BAC, in general one standard drink can be processed by the body in one hour.

The National Health and Medical Research Council recommends that people never drink above 10 standard drinks in a week, or four standard drinks in one day.

“The findings stress the need for state and federal governments to increase efforts in conveying the NHMRC guidelines on low-risk alcohol consumption,” says de Andrade.

If you’re concerned about your, or a friend’s, alcohol use, the Alcohol and Drug Foundation‘s Path2Help tool can help find resources.

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