Stats Chat

The Herald is reporting a WHO report that says the average levels of particulate air pollution are higher in Auckland than in New York.   The Environment Minister doesn’t believe it, and I tend to agree with him.

As the Green Party correctly points out, Auckland has far too many cars on the road.  But the same is true of New York, even though a larger fraction of their cars are taxis.  Auckland is surrounded by ocean, and the background levels of pollution in incoming air are very low.  New York is surrounded by a conurbation with a population of 21 million, nearly all of whom drive everywhere, and gets a substantial amount of pollution from the old coal-fired powerplants in the Ohio Valley.   Yes, the Northwestern Motorway is full of cars, but have you seen the Jersey Turnpike? (more…)

Or, as we would say, a statistician.

When you have too much data for Excel to handle: data scientists know how to deal with large data sets.

When your data visualization skills are being stretched: as we will see, data scientists are skilled (or should be) at data visualization and should be able to figure out a way to visualize most quantitative things that you can describe with words.

When you aren’t sure if something is noise or information: this is a big one, and we will come back to it.

Read the rest at  Mathbabe

This from TV3 news:

It’s not just rugby fans who are caught up in Cup fever.

An Auckland University professor has been predicting the results and so far he’s had an impressive success rate.

So does he think the All Blacks will win the World Cup? And how will the Warriors do in the NRL Grand Final on Sunday?

See the TV3 clip here.

Thank you for the large number of nominations for last week’s Stat of the Week competition.

This week’s winning statistic was first nominated by Deepika Sulekh:

Women who eat low-fat yoghurt while pregnant increase their chances of having children who develop asthma and hay fever.

Daily yoghurt consumption raised the odds 1.6 times of giving birth to a child who suffered from asthma by the age of seven.

We plan to write up some thoughts on this study once the paper is published and we’ve had a read. In the meantime read this blog post over at Junk Science.

(Special mention must go to Natalie’s comments about the “one in 3200 chance of the space junk hitting SOMEONE”.)

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:

• Anyone may add a comment on this post to nominate their Stat of the Week candidate before midday Friday September 30 2011.
• Statistics can be bad, exemplary or fascinating.
• The statistic must be in the NZ media during the period of September 24-30 2011 inclusive.
• Quote the statistic, when and where it was published and tell us why it should be our Stat of the Week.

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:

• Judging will be conducted by the blog moderator in liaison with staff at the Department of Statistics, The University of Auckland.
• The judges’ decision will be final.
• The judges can decide not to award a prize if they do not believe a suitable statistic has been posted in the preceeding week.
• Only the first nomination of any individual example of a statistic used in the NZ media will qualify for the competition.
• Employees (other than student employees) of the Statistics department at the University of Auckland are not eligible to win.
• The person posting the winning entry will receive a $20 iTunes voucher.
• The blog moderator will contact the winner via their notified email address and advise the details of the $20 iTunes voucher to that same email address.
• The competition will commence Monday 8 August 2011 and continue until cancellation is notified on the blog.

The ‘Big Wednesday’ lottery has moved from 6 balls out of 45 to 6 balls out of 50, which reduces even further the chance of getting the division 1 prize.  To win division 1, you need 6 balls correct out of 6, plus a correct coin toss.  There are 8,145,060 ways to choose 6 balls out of 45, and about twice as many ways, 15,890,700, to choose 6 balls out of 50.  Adding in the coin toss halves the chance of winning: the chance of winning per ‘line’ used to be 1 in 16,290,120 and is now 1 in 31,781,400.   For a minimum $4 ticket, which gives 4 ‘lines’, the chance of a division 1 prize was 1 in 4,072,530 and is now 1 in 7,945,350.

One back-of-the-envelope way to get roughly the correct impact of the change is to note that the chance of matching a given ball has gone down about 10%: from 1/45 to 1/50.  Multiplying 90% by itself six times says that the chance of winning is 53% of what it was, a very good approximation to the actual ratio, which is 51%.  The Dominion Post had the correct change, but the computations they report seem to have the effect of the coin toss backwards, so all their probabilities are overly optimistic by a factor of four.

Of course, the other way to look at it is that your chance of not winning division 1 with a $4 ticket has gone from 99.99998% to 99.99999%. Hardly seems worth mentioning. (more…)

Which do you think is more likely to kill you? A toaster or Islamic extremist terrorism? The answer may surprise you.

Security guru Bruce Schneier has written a piece entitled Terrorism in the U.S. Since 9/11. As a critic of the excesses of the United States of America’s response to the events of September 11, 2001, Schneier compares the spending on anti-terrorism with the number of lives saved.

In my opinion, the most interesting part was where he refers to a Comparison of Annual Fatality Risks published deep inside Hardly Existential: Terrorism as a Hazard to Human Life by John Mueller and Mark G. Stewart:

You have a 1 in 1,500,000 chance of being killed by a home appliance every year in the United States, but only a 1 in 3,500,000 chance of being killed by terrorism.

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 …