The Federal Reserve Bank of St Louis (part of the US Federal Reserve), who run the excellent FRED economic data website, have now released a free iPhone/iPad app that lets you download depressing economic statistics and graphics wherever you are.
There probably aren’t many people in New Zealand who would want this, but I bet they are over-represented among our readers.
New vaccines only get approved after randomized controlled trials showing that they are beneficial, but if you want to estimate the benefit of expanding vaccination to a new group of people it’s hard to do a randomized trial. Just comparing vaccinated and unvaccinated people doesn’t help, since there are many reasons why these groups are different, and the comparison gives completely unreasonable estimates. There’s a new study from Canada, reported by Reuters, that takes advantage of a ‘natural experiment’ to estimate the benefit of vaccinating children aged 2-4.
In the US, the guidelines on vaccination changed in 2006 to include kids in this age range, in Canada the guidelines didn’t change until last year. This allowed the researchers to compare hospital emergency room visits in Montreal and Boston and estimate the impact of the change. Just looking at US hospitals wouldn’t be enough, since there is a lot of year-to-year variation in the severity of the current flu strains, and just comparing the US to Canada wouldn’t work, since there are a whole lot of differences between the countries (starting with a national health insurance system). But looking at how the US:Canada difference changed from before 2006 to after 2006 gives a reasonable estimate of the effect of vaccination.
Looking at over 100,000 emergency-room visits for flu-like illness, researchers found a 34% decrease in risk for the 2-4 year age group affected by the change in guidelines. This wasn’t just for kids who were actually vaccinated — it also includes the reduction in risk from having your playmates vaccinated. There was a smaller reduction in risk, 10-20%, for older children — either because the additional reminders made them more likely to get vaccinated, or because they were less likely to catch flu from younger siblings.
Natural experiments get used a lot in economics. In medicine, we tend to prefer real experiments, but sometimes these are impractical or unethical, and natural experiments are the best we can do.
The estimate of 150,000 to 200,000 revellers at the waterfront for Rugby World Cup’s opening night has been dismissed by a statistician who calculated that it was a physically impossible to fit that number in the downtown entertainment areas.
Government and council officials said this week the waterfront was swamped by up to 200,000 people on September 9, leading to crowd control problems and transport failures.
Statistician Tony Cooper, the managing director of research company Double Digit Numerics, found the true figure was probably less than half that number. He estimated a maximum of 70,000 revellers in the lower CBD area.
Read more of this Weekend Herald story (17 Sept 2011) here …
Each week, we would like to invite readers of Stats Chat to submit nominations for our Stat of the Week competition and be in with the chance to win an iTunes voucher.
Here’s how it works:
Next Monday at midday we’ll announce the winner of this week’s Stat of the Week competition, and start a new one.
The fine print:
If you’d like to comment on or debate any of this week’s Stat of the Week nominations, please do so below!
No winner this week due to a lack of nominations – please add your suggestions for this week’s competition!
The factoid of dramatically increasing cannabis potency has popped up again, with a claim that cannabis used to be 1-2% THC and is now up to 33%. The most comprehensive and consistent data on cannabis potency come from a long-term project at the University of Mississippi. Their 2010 paper is based on analysis of 46,000 confiscated samples from 1993 to 2008. Over this time period, the percentage of THC in marijuana (leaves and buds with seeds) increased from about 3.5% to about 6%. The percentage in sinsemilla (buds without seeds) increased from about 6% to about 11%. Since the more-recent samples were more likely to be sinsemilla, the percentage over all confiscated samples increased a bit more, from about 3.5% to about 9%. A small fraction of the samples had much higher concentrations, but this fraction didn’t change much over time. So, yes, the average used to be about 3% in 1993 and may have been as low as 2% in earlier decades, and, yes, the concentration is now ‘up to‘ 33%, but the trend is nothing like as strong as that suggests. A New Zealand paper , by ESR researchers (who are hardly pot-sympathising hippies), says that there was no real change in THC concentration in cannabis plant material from 1976 to 1996, and the concentration in cannabis oil actually fell.
The Southland Times article also reports a claim that 90% of first-term methamphetamine users continue to use the drug. If this just means that 90% of them go on to have a second dose at some time it might well be true, but if it is implying long-term addiction the figure seems implausible. It’s certainly not what is found in other countries. For example, the most recent results from the US National Survey on Drug Use and Health (NSDUH) estimate that 364000 people in the US had dependence/abuse of illegal stimulants in 2010. If we assume that all of these were methamphetamine, and that the other illegal stimulants didn’t cause any dependence/abuse problems, that’s still only 20% of the estimated 1.8 million people who first tried methamphetamine in the period 2002-2010. In fact, since NSDUH has a nice online table generator we can do a more specialized query and find out that an estimated 118000 people currently had dependence on stimulants out of the estimated 10 million people who had ever tried methamphetamine. That’s more like 1% than 90%. Amphetamines are clearly something you want to stay well away from, but there’s no way that they addict 90% of the people who try them. In any case, if we believe the drug warriors, New Zealand’s P epidemic has already been solved by banning pseudoephedrine without a prescription.
I’m all for getting teenagers to appreciate the risks of drug use, but we need to remember teenagers can use Google too.
Last week’s Stat of the Week nomination was a story on the “J-curve” for disease risk and alcohol consumption. Yet another research paper, this time from the Nurses’ Health Study, had found that people who drink small amounts of alcohol regularly are healthier than those who drink none and those who drink larger amounts. This sort of result is unpopular with doctors, as the Herald story reported, and for good reasons, but that doesn’t mean it’s untrue. On the other hand, the fact that it’s true doesn’t mean that it’s news.
The obvious difficulty in comparing drinkers to non-drinkers is that some of the strictest non-drinkers are actually ex-drinkers, people who you would expect to be in worse health. Since epidemiologists are not completely stupid, they know about this problem and many studies have addressed it. Excluding ex-drinkers doesn’t make the effect go away, waiting for a long time between the drinking assessment and the health assessment (as in this paper) doesn’t make it go away, and splitting up light drinking into finer categories shows that there is lower risk for people who drink occasionally than for those who regularly drink a small amount (again, as in this paper). For some of the claimed benefit there are even plausible mechanisms (eg, alcohol consumption does definitely raise HDL cholesterol levels in short-term experimental studies). This is just observational research, so the results could be just as wrong as the apparent protective effect of beta-carotene in cancer, or of raising HDL cholesterol with niacin in heart disease, which fell apart when subjected to randomised trials, but it’s carefully-done observational research.
As doctors will tell you, the problem with announcing a health benefit of moderate alcohol consumption is that most people interpret “moderate” to mean “a bit more than I currently drink”. As a scientific result, it’s fine; as a public-health intervention, it’s badly off-target. The American Heart Association guidelines on alcohol and heart disease, for example, basically say that regular consumption of small amounts of alcohol probably is protective against heart disease, but that you shouldn’t go around advocating it.
The problem for medical researchers is that funding bodies and universities (and their own egos) want press coverage of research results, but that this sort of marketing of incremental medical research as if it was ground-breaking health advice is unhelpful to the public. It’s very rare that you should change your behavior based on the results of a single medical study, but that’s the model that a lot of medical reporting is based around.
Congratulations to Eric Crampton for another great nomination and we have awarded it as our winner. It’s a fairly technical, well-researched Stat of the Week which is argued well.
Each week, we would like to invite readers of Stats Chat to submit nominations for our Stat of the Week competition and be in with the chance to win an iTunes voucher.
Here’s how it works:
Next Monday at midday we’ll announce the winner of this week’s Stat of the Week competition, and start a new one.
The fine print: