Think you can estimate how drunk you are? You’re wrong, scientists say
Drinkers leaving bars and heading for their cars got an unpleasant surprise in Los Angeles recently: police officers waving a breathalyzer in their faces and asking to check their blood alcohol concentration (BAC). But the drinkers weren’t being arrested for driving while drunk. In fact, the police were actually protecting them from being arrested.
The voluntary breathalyzer tests were part of a campaign that was cleverly designed to educate the public about a simple fact: we’re really bad at knowing how drunk we are.
“Most drinkers were surprised by how high their blood alcohol content was”, said Lieutenant Mark Rossi of the Riverside Police Department, which managed the tests. “One guessed his alcohol level was .04 percent. His actual BAC was .12 percent”. The legal limit for an automatic DUI (Driving Under the Influence) arrest is .08 percent. After the test, police helped that driver, and other drunk drivers, to call a cab, or find other means of getting home safely.
The science of drunkenness
That police officer’s experience is backed up by scientific fact. Numerous studies show how bad we are at estimating our blood alcohol levels. For example, researchers in Australia offered free breathalyzer tests to hundreds of drivers who were leaving a bar at midnight and intending to drive home. Once they saw the breathalyzer results, one third of those drivers changed their minds and decided not to use their cars – because the tests showed them they were actually over the legal limit, and they hadn’t even realized.
When drinkers are asked to estimate their own BAC, studies show that about a third are confident they can guess the approximate figure. But an incredible 90 per cent of them get it wrong. In fact, they aren’t simply wrong, their guesses are off by 50 percent, on average.
What this means is that huge numbers of drinkers get behind the wheel believing they’re good to go, when in fact they’re breaking the law and at heightened risk of causing injury or death. In the US alone, 10,000 traffic fatalities every year involve drunk drivers – that’s over a third of all traffic deaths. One person is killed by a drunk driver every hour, on average.
Why are we so bad at knowing how drunk we are?
The dangers of drunken driving are obvious, so why do people still do it? As researchers have found, it’s often because drivers just don’t realize they’re seriously impaired. We’re terrible at estimating how much alcohol is in our blood, mainly because there are so many factors involved. It’s not just about how many drinks you’ve had.
Obviously, the amount of alcohol you’ve consumed and the amount of time since your last drink are the biggest contributors to blood alcohol level. But there are also many other variables influencing how drunk you are: the strength of the drinks, your weight and body fat ratio, how much you’ve had to eat, what you ate, and more.
It’s difficult enough keeping track of all those factors, and it only gets harder when your judgment is affected by alcohol. “The failure to recognize alcohol impairment is often a symptom of alcohol impairment,” warns the US Department of Transportation, soberly.
How can we estimate our own BAC?
There are various methods for trying to estimate your BAC by yourself. For example, counting how many drinks you’ve had, estimating their strength, and then combining that information with your personal stats, such as your height, weight, sex and age. There are even mobile apps that claim to help. However, these methods are not only complicated, but of questionable accuracy. For easy, on-the-spot measurement of BAC, a breathalyzer is still the gold standard.