A while back the Global Drug Survey (GDS) produced its annual report. Here are some of the newspaper headlines following its publication:
And reading some of these articles in detail we find:
- Of the 31 countries included in the study, Britons get drunk most regularly (51.1 times per year, on average).
- Britain has the highest rate of cocaine usage (74% of participants in the survey say they have used it at some point).
- 64% of English participants in the survey claim to have used cocaine in the last year.
Really? On average Brits are getting drunk once a week? And 64% of the population have used cocaine in the last year? 64%!
Prof Adam Winstock, founder of the survey, summarises things thus:
In the UK we don’t tend to do moderation, we end up getting drunk as the point of the evening.
At which point it’s important to take a step back and understand how the GDS works. If you want a snapshot of a population as a whole, you have to sample in such a way that every person in the population is equally likely to be sampled. Or at least ensure by some other mechanism that the sample is truly representative of the population. But the Global Drug Survey is different: it’s an online survey targeted at people whose demographics coincide with people who are more likely to be regular drinkers and/or drug users.
Consequently, it’s safe to conclude that the Brits who chose to take this survey are likely to get drunk more often than people from other countries who also completed the survey. And that 64% of British participants in the survey have used cocaine last year. But since this sample is neither random nor designed to be representative, it really tells us nothing about the population as a whole. And even comparisons of the respondents across countries should be treated cautiously: perhaps the differences are not due to variations in drink/drug usage but instead due to variations in the composition of the survey respondents across countries.
Here’s what the GDS say themselves about this…
Don’t look to GDS for national estimates. GDS is designed to answer comparison questions that are not dependent on probability samples. The GDS database is huge, but its non-probability sample means analyses are best suited to highlight differences among user populations. GDS recruits younger, more experienced drug using populations. We spot emerging drugs trends before they enter into the general population.
In other words, by design the survey samples people who are more likely to drink regularly or to have used drugs, and the GDS itself therefore warns against the headline use of the numbers. It’s not really that 64% of the UK population that’s used cocaine the last year; it’s 64% of a self-selected group who are in a demographic that are more likely to have used cocaine and who responded to an online survey.
To emphasise this point the GDS information page identifies the following summary characteristics of respondents to the survey:
- a 2:1 ratio of male:female;
- 60% of participants with at least a university degree;
- an average age of 25 years;
- more than 50% of participants reporting to have regular involvement in nightlife and clubbing.
Clearly these characteristics are quite different from those of the population as a whole and, as intended by the study, orientated towards people that are more likely to have a drinking or drug habit. At which point the newspaper headlines become much less surprising.
Now, there’s nothing wrong with carrying out surveys in this way. If you’re interested in attitudes and behaviours among drinkers and drug users, there’s not much point in wasting time on people who indulge in neither. But… what you get out of this is a snapshot of people whose characteristics match those of the survey respondents, not of the population as a whole. And sure, this is all spelt out very clearly in the GDS report itself, but that doesn’t stop the tabloids (and even the Guardian) from headlines that make it seem like Britain is drink/drug capital of the world.
- You can extrapolate the results of a sample to a wider population only if the sample is genuinely representative of the whole population;
- The best way of ensuring this is to do random sampling where each member of the population could be included in the sample;
- The media aren’t going to let niceties of this type get in the way of a good headline, so you need to be extremely wary when reading media reports based on statistical surveys.
What seems to be a more scientific approach to studies in the variation of alcohol consumption across countries is available here. On this basis, at least in 2014, average alcohol consumption in the UK was considerably lower than that in, say, France or Germany. That’s not to say Brits got drunk less: it might still be that a proportion of people drink excessively – to the point of getting drunk – but the overall average is still relative low.
However, if you look down the page there’s this graph…
…which can be interpreted as giving the proportion of each country’s population – admittedly in 2010 – who had at least one heavy night out in a period of 30 days. France and the UK are pretty much level on this basis, and not particularly extreme. Lithuania seems to be the most excessive European country in these terms, while king of the world is apparently Madagascar, where 64.8% of the population reported a heavy drinking session over the 30 day period. So…
It’s official: Madagascans get drunk more often than anywhere else in the WORLD