Tuesday, 31 August 2010

How good are we at estimating other people's drunkenness?

Sloshed, trollied, hammered, plastered. We've done a sterling job of inventing words for the inebriated state, but when it comes to judging from their behaviour how much a person has drunk, we could do (a lot) better. That's according to a review of the literature by US psychologist Steve Rubenzer.

We all have our trusted indices for judging other people's drunkenness. Perhaps it's when the eyeballs start floating about as if under the control of a clumsy puppeteer. Or maybe the effusive 'you know I love you' delivered with a trickle of dribble. However, the vast majority of studies find that lay people, police officers and bartenders are in fact hopeless at distinguishing a drunk person from a sober one, at least at moderate levels of intoxication. To take just one example, after watching drunk and sober people being interviewed and negotiating a stair case, bartenders rated them as slightly, moderately or very drunk with an accuracy of just 25 per cent.

It's a similar story when participants are equipped with more structured means of detecting drunkenness. One 1958 study, for example, found no relation between doctors' assessments of people's intoxication (based on pulse rate, general appearance, gait and mental status) and the subsequent performance of those people on a driving course.

Rubenzer also looked at the evidence for specific indicators of intoxication. Alcohol causes reddening of the eyes, the literature shows, but the association between intoxication level and onset or amount of redness is unreliable. Another indicator is smell. The more a person has drunk, the more likely that their breath will be judged by observers to smell of alcohol. However, this indicator is hampered by the lack of a scientific explanation (alcohol has no odour), not to mention the risk of contamination by food smells. Speech slowing and slurring is another sign of intoxication but people are only modestly accurate at using this as a measure. Predictably enough, impaired walking, the last of the specific indicators, tends to increase the more a person has drunk but it only becomes reliable at very high intoxication levels.

The review finishes by looking at established 'sobriety tests': Nystagmus (jerky eye movements when following a moving target); the Romberg (whether a person sways or falls when they stand, eyes closed, with their feet together, arms at their sides); the Finger to Nose; the Finger to Finger; Saying the Alphabet; and the Hand Pat (alternating between clapping with the palms and backs of hands). In summary, performance on these tests does tend to decline as alcohol intake increases but the evidence for this at lower levels of intoxication is mixed and false positives (sober people categorised as drunk) are a frequent occurrence.

'...[J]udging low to moderate levels of intoxication in strangers is a difficult task,' Rubenzer concludes. 'A variety of professions that might be expected to show substantial skill assessing intoxication do not. [And] no behavioural or physical sign has emerged that is consistently related to a specific level of blood alcohol concentration level without large variation among individuals, with the possible exception of nystagmus.'

ResearchBlogging.orgRubenzer, S. (2010). Judging intoxication. Behavioral Sciences & the Law DOI: 10.1002/bsl.935

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.


Rob said...

Two points:

(1) For bar tenders and police officers, surely it's the behaviour itself which is important, not the underlying blood alcohol concentration. They can see when a person has had enough or is causing a nuisance, without any need to know objectively how much they have drunk. (Of course it's different when we're talking about driving, which is why police have objective tools for testing drivers suspected of being over the limit.)

(2) "... smell of alcohol ... this indicator is hampered by the lack of a scientific explanation (alcohol has no odour) ..."
That's a very strange comment. Pure alcohol may have no odour, but beer and wine certainly do.

Matt Matson said...

From the abstract: "It is concluded that observers relying on common-sense clues of intoxication have limited ability to assess the blood alcohol concentration (BAC) levels of strangers, particularly below .10%."

The post assumes that blood alcohol concentration (BAC) levels = drunkenness. Is this appropriate? As a matter of communication, when someone is described as drunk, I understand that to mean the person is exhibiting symptoms related to consuming alcohol, not that their BAC is elevated beyond a specified level.

If anything, this article suggests that BAC is not a good way to determine actual drunkenness because there are "wide variations between casual social drinkers and those that have obtained a high level of tolerance."

The author is concerned about an observer's ability to determine whether a person has crossed a legal BAC threshold. And, given the law, it might be considered unfair to find a person guilty of driving under the influence when the person has not had much to drink and does not have a high BAC, but fails a sobriety test. On the other hand, what society is concerned about is not that people with high BAC's are driving, but that impaired individuals are driving. If a person is impaired at a low BAC, should they be driving? Perhaps light drinkers should be held to a lower BAC standard.

Nikki said...

pssst... It's color that (pure) alcohol doesn't have, not odour. Ethanol's odour is quite strong. Open a container and smell for yourself, but make sure you're sober when you do, because in the inebriated state you may indeed not feel it, the same way you stop perceiving your own perfume within minutes of applying it.

Aaron said...

I'm a bartender and and economics student. I can tell you from experience that it is typically difficult to tell how intoxicated a person is. Besides the fact that people react to alcohol differently, a person's intoxication level may increase for a period of time after they have stopped consuming because it takes time for alcohol to be absorbed.

Scott said...

Well, duh. As a bartender, I have to say that all the training in the world (by the way, there is none) doesn't make it easier to spot someone who is mildly (or mostly) intoxicated. That isn't usually the point. In fact, or opinion, the point of drinking for most people is to become inebriated to a greater or lesser degree and over time folks simply get better at it. There are no absolute external indicators unless someone is so bombed even an amateur can spot it.

Unknown said...

Even pure abs. alcohol has an odour. At 99.86% it has an odour. Denatured alcohol does smells also. This smell is the presence of a bittering agent which renders the alcohol unfit for human consumption. In short does smell/. I agree with Nic(ki). (sorry for the British Political joke)

Unknown said...

oh another thought occurred; due to habituation and smell saturation of the olfactory nerves - a barman is probably a really poor person at being able to judge, by smell, if someone has been drinking.

Anonymous said...

The article didn't once mention BAC, perhaps you meant to comment on a different one.

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