Posts from August 2011 (37)

www.kaggle.com hosts many data mining and statistical prediction competitions, some with big prizes (USD10,000+). Have you got what it takes to win?

Thank you Eric Crampton for another great nomination for this week’s Stat of the Week competition, but due to a lack of other entries we will not be awarding a winner this week.

Please add your nominations for the new competition, there are plenty of Stat of the Week candidates out there!

Thomas Lumley was interviewed at length on the most recent edition of Mediawatch (Radio New Zealand, Sundays 9.05am) talking about the “TV kills you” post (he was also asked about many of the other things that annoy statisticians about the media).

Listen from 21.40 on.

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 2 2011.
• Statistics can be bad, exemplary or fascinating.
• The statistic must be in the NZ media during the period of August 27-September 2 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.

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

News stories about monthly counts of road deaths, suicides, or other relatively rare events tend to cause statisticians to grind their teeth and mutter “Poisson variation”.  If you have two deaths a week  apart, some of the time they will fall in the same month and some of the time in different months, pretty much at random.  This makes the monthly totals very variable: if Christchurch averages about 7 suicides per month and there was nothing making this vary over time, you would expect in most years to see a month with as many as 11 suicides and another with as few as three.  That sort of variation is unavoidable, and doesn’t indicate that there is anything to explain.  It’s called “Poisson variation” because the “nothing to see here, move along” distribution for counts was investigated in the 19th century by French mathematician Simeon Denis Poisson, in a study of court judgments.

With only Poisson variation, a month with just one suicide would be very unusual, though. Only one month in 12 years would we be that fortunate if nothing but chance were operating.  The NZ Herald is quite right that suicide rates have been down in Christchurch — there is something to explain, and the explanation is reasonable. The Dominion Post does even better, giving multiple possible explanations for the dip.

The papers do lose points for not linking to the actual numbers released by the Chief Coroner, which I still haven’t been able to find.

Hurricane Irene is heading for somewhere on the US East Coast, though it’s not clear where.  Weather Underground has a nice range of displays indicating the uncertainty in predictions of both location and storm intensity.

Today’s NZ Herald reports that Māori and Pacific Islanders are highly represented in the statistics for the use of tasers by the NZ police. Green MP Keith Locke is quoted as saying “Certainly they’re being fired disproportionately at Māori.” Mana Party spokeswoman Annette Sykes is quoted as saying “there has been this disproportionate outcome for Māori and Polynesian individuals, which is a sad indictment on us.”

Looking at the numbers, a taser has been used 35 times out of a total of 88 on Māori, or just under 40%. This is certainly much higher than 15% reported for the percentage of Māori from the 2006 census. However, this is not the relevant population. Rather, we should consider the proportion of Māori involved in the criminal justice system.

Figure 1, on page 17 of the report on Identifying and Responding to Bias in the Criminal Justice System: A Review of International and New Zealand Research (Bronwyn Morrison, Ministry of Justice 2009: p17) shows that approximately 40% of individuals involved New Zealand criminal justice system (in 2006) were Māori. These figures support the statement by Police Minister, Judith Collins that “the figures merely reflect the “sad fact” that Māori are over-represented in crime statistics.”

For those of you who like the statistics, then assuming a binomial model, the probability of observing 35 or more out of 88 incidents with p = 0.4, is approximately 0.47.

What do we take from this? Māori are not over-represented in the taser statistics. They occur in almost exactly the same proportion as they do in all other aspects of the criminal justice system.

No, not last week’s snow.  To paraphrase Crocodile Dundee: “That’s not an extreme weather event! This is an extreme weather event.” The graph below shows daily deaths in Chicago, over a fourteen year period.  Do you notice anything?

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Minimum amount of physical activity for reduced mortality and extended life expectancy: a prospective cohort study »