Posts from March 2012 (64)

Team Ratings for Round 4

Here are the team ratings prior to Round 4, along with the ratings at the start of the season. I have created a brief description of the method I use for predicting rugby games. Go to my Department home page to see this.

Performance So Far

So far there have been 24 matches played, 12 of which were correctly predicted, a success rate of 50%.
Here are the predictions for the games so far.

Predictions for Round 4

Here are the predictions for Round 4

Team Ratings for Week 5

Here are the team ratings prior to Week 5, along with the ratings at the start of the season. I have created a brief description of the method I use for predicting rugby games. Go to my Department home page to see this.

Performance So Far

So far there have been 27 matches played, 16 of which were correctly predicted, a success rate of 59.3%.
Here are the predictions for last week’s games.

Predictions for Week 5

Here are the predictions for Week 5. The prediction is my estimated points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.

In one of our Stat of the Week nominations, the commenter takes issue with ” There is an incident [of intimate partner violence] reported to the police every 7 minutes and only 18% of cases are reported”

According to this there are 417,000 instances of physical intimate partner violence every year. With a population of around 4 million, and half women, this means that up to 40% (bad stat alert!) could be affected every year.

Leaving for the moment whether the 18% reporting rate is well-founded,  the ‘up to’ is critical here.  If the occurrences were independent, 417,000 instances would be 40%of NZ women, but of course they aren’t independent.  People don’t just abuse their partners once, they keep doing it until they are stopped.  With 417,000 instances, the actual number of women attacked per year could as easily be 4% as 40%.

A similar issue came up with the elimination of TV7, when Jonathan Coleman divided the number of monthly viewers of TV7 by four and called it an estimate of weekly viewers.  That would be appropriate if watching TV7 one week was independent of watching it the next week, but of course it’s not.  The real number of weekly viewers will be very close to 100% of the number of monthly viewers, not 25%.

The issue is very important in legal settings.  British paediatrician Roy Meadow famously wrote (and testified in court) “one sudden infant death is a tragedy, two is suspicious and three is murder, until proved otherwise”.  If sudden infant deaths were independent, then three in one family would be very rare, but we don’t have good evidence that they are independent.  On top of this,  multiple murder of infants, especially without leaving any signs, is also rare: knowing that a rare thing happened doesn’t tell you which one it was.

What provoked this post, though, was a reader’s email reminding us of the joke about the man who always carried a bomb when he flew, on the grounds that two bombs on the same airline would be incredibly unlikely.  The point of the joke is that his bomb obviously seems independent of a hypothetical other bomb, so the safety is unaffected.  In fact, if you manage to carry a bomb onto a plane it’s either a small regional NZ flight that doesn’t have screening, or there’s been a failure of the security system.  While it’s not terribly worrying that the security system failed, it does make you wonder what else isn’t being done according to plan. Perhaps you should reconsider your flight plans.

From a talk I’m giving tomorrow to the Canterbury Mathematical Association:

“Bogus polls look a bit like real surveys on the outside, but don’t have any of the inner machinery that you need to make them work.”

A Campbell Live trailer just asked “Why is the disease that’s at epidemic levels about to be targeted by government cuts?”

In what is unfortunately an urban legend, Willie Sutton was supposedly asked “Why do you rob banks?”, and replied “Because that’s where the money is”.

There is no point in the NZ medical system spending too much time and effort on assessing cost-effectiveness in idiopathic pulmonary fibrosis, Fabry syndrome, or Hashimoto’s encephalitis.  Reducing the cost of diabetes treatment, on the other hand,  can free up a lot of money to spend on other illnesses.  There’s nothing surprising or shocking about targeting diabetes for cost savings, especially in a low-cost public health system like ours.

The real question is whether the savings in money come at too high a price in patient care, not why diabetes is one of the targets.

This week’s installment in the stream of stories that have found The Answer To Obesity says the problem isn’t just diet or exercise, it’s plastic bottles.   The Herald says

Man-made chemicals present in homes, schools, offices, cars and food are probably contributing to the sharp rise in obesity and diabetes in Western societies, according to a review of scientific literature published yesterday.

Until now lifestyle factors such as lack of exercise and poor diet were believed to be the primary causes of the increased incidence of both conditions, whose proliferation has strained global health budgets.

If you separate out diabetes, it’s not true that obesity has strained global health budgets.  The incidence of heart attacks, for example, continues to go down all over the world.  The rate of decline has slowed a bit, but increases are still theoretical and aren’t straining anything.  However, if we stipulate that obesity is bad, are bisphenol A, PCBS, and phthalates responsible?

All 240 studies they reviewed – whether in test-tubes, on animals or on humans – had been peer-reviewed and published in scientific journals.

It occurred to me that using the bus prediction system to estimate traffic congestion would make a nice student research project.  Bus flow along Dominion Rd or through Newmarket, say, gives a lot of information about traffic congestions.  This information might be useful for improving bus predictions, but also might be useful for drivers as a way of getting real-time congestion data for a much larger set of roads than is currently available.

Unfortunately, the terms of use for the prediction system say “No part of the MAXX Website may be distributed, resold, published, copied, reproduced, transmitted or stored and you are not permitted to incorporate the material or any part of it in any other work or publication (whether in hard copy, electronic or any other form) without ATs express written consent.”  I’m not sure if this is actually true, but it’s a fight I don’t need to have.

Stuff is reporting a survey on attitudes to overseas ownership of NZ farms.   New Zealanders aren’t just opposed to Chinese buyers of the Crafar farms because they’re racist — they say so themselves.

According to the story, the survey asked

“The Chinese company Shanghai Pengxin wants to buy the Crafar farms; do you support or oppose selling the farms to this Chinese company?”

and then

“Do you agree, or disagree, with this statement: ‘I don’t care what the nationality of the company is, I don’t want the farms to be sold to a foreign buyer’.

Not surprisingly, people who had said they didn’t want Shanghai Pengxin as the buyer went on to say that it wasn’t just Chinese buyers they were opposed to.

If you really want to find out whether people feel differently about a Chinese buyer, this isn’t the best way.  You want to ask different samples of people about Chinese buyers and buyers from, say, the UK, or Monaco, or some other country with more NZ farm ownership than China.   That way, people’s natural reluctance to admit to anti-Chinese bias won’t distort the results.

A survey like that would actually be interesting, since it’s not at all clear whether anti-Chinese bias is a big factor or a small one.

Thanks to Cam for his nomination of child abuse statistics – there’s some discussion in response. Due to a lack of other nominations, we are not awarding a winner this week. Please add your nominations again to this week’s competition!

We don’t get a lot of opportunities to say nice things about statistics in the press, but the Herald has a good example today in a report on young Maori health.  They report both the numbers of hospital admissions for Maori and non-Maori, and the relative risk.   It wouldn’t hurt if they had linked to a definition of bronchiectasis, though.