Is cocaine use actually up in the EU?

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What's the one piece of information you would expect to have in an article entitled "Report: Cocaine use up in Europe"? That's right, how much it's up. Unfortunately, that's the one piece of information you don't get in this article.
About 9 million people in the European Union, 3 percent of all adults, have tried cocaine, while up to 3.5 million are likely to have to have used it in the last year and 1.5 million took the drug in the past month, the report found.

"Historically, cocaine was a fairly rare drug in Europe," said Paul Griffiths, scientific coordinator for the European Monitoring Center for Drugs and Drug Addiction, which published the survey. "Then in Britain, the Netherlands and Spain it became increasingly available in big cities and now it is very visible in national statistics in these countries and our concern is there could be further diffusion in Europe," he said.

In Britain and Spain, more than 4 percent of 15-34 year-olds consumed cocaine in the past 12 months, close to the level in the United States, where cocaine has been a problem for longer than in Europe, the report said. In those two countries, the number of young adults taking cocaine, often described as a trendy recreational drug, exceeded those using ecstasy and amphetamines.

Despite the rising trend in Britain, the growth in cocaine use there appears to be stabilizing at historic high levels while other EU members such as France show signs of catching up, Griffiths said.

The impact of increasing cocaine use is also showing up in health statistics. Although deaths attributed to cocaine use alone are rare, the drug played a role in 10 percent of all drug-related deaths, meaning there could be several hundred deaths per year linked to cocaine in the 25-nation bloc, the report said.

Worse yet, it's not in the EU's press release, which leads with the same cocaine use is up message.

However, if you read the actual report, you get a quite different picture of the sitation. Here's the relevant summary:

Clear-cut European trends in cocaine use, based on population studies, are still difficult to identify (see section on cannabis trends). However, warnings about increases in cocaine use in Europe have come from several sources, including local reports, focused studies conducted in dance settings, reports of increases in seizures indicators and some increases in indicators related to problems (deaths, emergencies). Recent cocaine use among young people increased substantially in the United Kingdom from 1996 until 2000,

but has remained relatively stable since then, although moderate increases have been observed in recent years, and in Spain (91) from 1999 to 2001. Less marked increases were observed in Denmark, Italy, Hungary, the Netherlands and Austria (in local surveys) and, with oscillations over the 1990s, in Germany (Figure 11).

And turning to Figure 11 (last-year usage for 15-34), we see a figure that doesn't even remotely show an overall increase:

At best, this figure would let you claim that cocaine use is up from the mid 1990s in some countries. The big, clear, trend, is in the UK, but even there it's pretty misleading to say that cocaine use is "up". More accurate would be to say that there was a big jump from 1994-2000 and then things have been pretty flat since then. Indeed, lacking error bars on these figures, it's pretty hard to draw any real conclusions about the size or even existence of any increase since 2000.

Figuring that out requires going straight to the data set. Let's take the UK data. The sample size in 2004 was 8590 with 4.9% of users claiming to have used cocaine in the previous year. Working backwards, this tells us that they had 416 positive responses. Using standard formulas for the accuracy of a point estimate of population proportion, we get a point estimate of 4.9% (as expected) with a 95% confidence interval of (4.45%-5.35%). The rest of the data points (4.5% in 2000, 4.0% in 2001, and 4.3% in 2003) are from similar sample sizes, so this shouldn't give you a real warm feeling about claiming that use is "up" in the 2000-2003 time frame.

The summary of the French data in the Reuters report is even more misleading. The national French estimate for 1999 and 2000 (the only years for which there is data on cocaine) was .5%. The Metropolitan data is up from .4% in 1995 to .7% in 2002, but this is with a tiny sample size of 724, so the 95% CI is (.1%-1.3%) and you clearly can't draw any conclusions about a trend, and certainly not that France is "catching up" to the UK.1

As usual, there are two failures here. The first is that the researchers presented a not-that-accurate bottom line summary of their results without appropriate caveats about uncertainty or inter-country variation. The second is that the press accepted these results uncritically without bothering to go read the report itself. None of this is to say, of course, that cocaine use isn't up in the EU. Rather, we just can't tell that from this data.

1. There seems to be something funny about the France line, because Fig 11 appears to show totally different data points (and for different years) than are listed in the relevant table. I'm working from the table, but I may have missed something here. Not that the "trend line" in the graph is very convincing either.

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1 Comments

I don't think you understand. Any evidence that _might_ indicate a rise in cocaine use means we must do something! We need legislation that responds unequivocally to this threat. Anyone who says otherwise is for drugs. Think of the children!

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