Posts from April 2014 (60)

If you’d like to comment on or debate any of this week’s Stat of the Week nominations, please do so below!

The Herald story “Uni cheats: hundreds punished” is a pretty good example of using actual data to combat the ‘false balance’ problem in journalism.  The story notes the huge variation in official proceedings for cheating between NZ universities — nearly half the cases are at Waikato — and rightly highlights it as “suggesting differences in what institutions consider cheating, and how they target and record it.”

As the story doesn’t point out, with 540 cases out of more than 400000 tertiary students it’s pretty clear cheating is underreported everywhere. That’s hardly surprising, given the costs and benefits to staff for following it up. If it wasn’t for the irrational rage cheating arouses in academics, it would be perfectly safe.

From the Herald, in a good article about the Australian report on homeopathy

Auckland homeopath Suzanne Hansen said the treatments could not be measured in the same way medical treatments were.

“When you research it against a medical paradigm it will fail because you treat in a completely different way.”

This is probably true, but it’s a major concession that should be noted for the record.

The`medical paradigm’ of randomised controlled trials doesn’t need treatment to be the same for each person, it doesn’t need the benefits to be the same for each person, it doesn’t need the biological mechanism to be known or even plausible. All they need is that you can identify some group of people and a way of measuring success so that getting your treatment is better on average for your chosen group of people with your chosen way of defining ‘better’.  This isn’t just about homeopathy —  the whole field of personalised genomic medicine is based on individualising treatment, and this doesn’t introduce any difficulties for the medical paradigm.

If an intervention can’t beat fake pills that do nothing, on its choice of patient group and outcome measurement, it will fail when you `research it against a medical paradigm.’  If you’re fine with that, you should be fine with not using any advertising terms that suggest the intervention has non-placebo benefits.

• How Americans Die: infographics can actually be informative (via Rob Isaac)
• Let’s Experiment More: randomised experiments outside medicine
• UK Pensions Minister wants to send pensioners an estimate of when they will die, to improve their financial planning. I’m sure there’s no way this could go wrong.
• Ezra Klein interviews Mark Kleiman on cannabis legalisation.

Radio Yerevan jokes were a thing in the Soviet Union days

The Armenian Radio was asked: “Is it true that in Moscow, Mercedes cars are being given to citizens?”

The Armenian Radio answers: “Yes, but it is not Moscow but Leningrad, not Mercedes but Ladas, and not given to but stolen from.” 

From the Herald, yesterday

People who had only used cannabis once or twice a week for a matter of months were found to have changes in the brain that govern emotion, motivation and addiction.

Here’s the research paper, which you won’t be able to access, so I’ll summarisse

Firstly, no-one in the study was found to have ‘changes’ in the brain: the participants got only one brain scan, so the research didn’t even look at changes. It found differences between cannabis users and non-users. There’s nothing even slightly surprising about the possibility that people who end up as regular users of an illegal drug might have started off with brain differences.

There were 20 cannabis users in the study, who smoked an average of 11 joints per week, and had been smoking cannabis for an average of six years. Here’s the data for one of their findings, on ‘gray matter density in the nucleus accumbens’

The dots at zero are the controls, the other dots are the cannabis users. There certainly aren’t many who use cannabis only once or twice per week. It’s hard to tell whether there’s really anyone who has only used cannabis for a few months,  because the research paper only reports the mean and standard deviation for duration of use.

So, the main point of the story in the paragraph quoted above is completely unsupported by the research.  This one isn’t entirely the fault of the media, since the researchers were pushing hard to exactly this sort of unsupported claim into the papers.  Still, you might have hoped someone they talked to would have matched up the claims to the research..

This is not a map. The Asian population of the US is not confined to Maine and northern Washington, and residents of the Dakotas are not primarily Black and Hispanic. It’s a stacked line plot, which has been cut out to fit the map outline, just like you might do in kindergarten. (via Flowing Data)

Here’s the real thing, from Pew Research.

Team Ratings for Round 7

The basic method is described on my Department home page. I have made some changes to the methodology this year, including shrinking the ratings between seasons.

Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 48 matches played, 24 of which were correctly predicted, a success rate of 50%.

Here are the predictions for last week’s games.

Predictions for Round 7

Here are the predictions for Round 7. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.

Team Ratings for Round 10

The basic method is described on my Department home page. I have made some changes to the methodology this year, including shrinking the ratings between seasons.

Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 55 matches played, 34 of which were correctly predicted, a success rate of 61.8%.

Here are the predictions for last week’s games.

Predictions for Round 10

Here are the predictions for Round 10. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.

We learned previously from Stuff and the Global Drug Use Survey that 22% of New Zealanders have used synthetic cannabis. Today

Results from this year’s Global Drug Survey, conducted in partnership with Fairfax Media, found almost 4 per cent of synthetic cannabis users sought emergency medical treatment. More than a quarter of those were admitted to hospital.

It simply cannot be true that 4% of 22% of the country has sought emergency treatment after using synthetic cannabis. Even restricting to adults, that’s 30,000 people, with more 7,500 admitted to hospital. In the most recent year for which I can find data (2010-11, when the drugs were more widely available than now) there were 672,000 publicly funded hospital admissions for all causes, and of those, only 896 were for cause categories X41 & X42, which would include all synthetic cannabis cases plus many others.

[update: fixed typo in numbers]

That’s the online summary at Stuff.  When you point at one of the bubbles it jumps out at you and tells you what drug it is. The bubbles make it relatively hard to compare non-adjacent numbers, especially as you can only see the name of one at a time. It’s not even that easy to compare adjacent bubbles, eg, the two at the lower right, which differ by more than two percentage points.

More importantly, this is the least useful data from the survey.  Because it’s a voluntary, self-selected online sample, we’d expect the crude proportions to be biased, probably with more drug use in the sample than the population. To the extent that we can tell, this seems to have happened: the proportion of past-year smokers is 33.5% compared to the Census estimate of 15% active smokers.  It’s logically possible for both of these to be correct, but I don’t really believe it.  The reports of cannabis use are much higher than the (admittedly out of date) NZ Alcohol and Drug Use Survey.  For this sort of data, the forthcoming drug-use section of the NZ Health Survey is likely to be more representative.

Where the Global Drug Use Survey will be valuable is in detail about things like side-effects, attempts to quit, strategies people use for harm reduction. That sort of information isn’t captured by the NZ Health Survey, and presumably it is still being processed and analysed.  Some of the relative information might be useful, too: for example, synthetic cannabis is much less popular than the real thing, with past-year use nearly five times lower.