Posts filed under General (3156)

The Dominion Post has a story,  nominated for Stat of the Week, headlined “Wairarapa has best odds for tonight’s $22m Powerball”.

If this were true, it would imply serious fraud or incompetence by the people running Powerball.  The story doesn’t come out and say that explicitly.  What it says is

Sales and prize data provided to The Dominion Post by the Lotteries Commission show the Wairarapa region averaged the highest return per dollar spent last year.

The Herald asks “Is John Carter the biggest flop of all time?”

While there isn’t an official definition of `flop’, it’s worth noting that John Carter has grossed $184 million in two weeks.  That’s quite a lot of money. For example, it’s more than the first Harry Potter movie managed.

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.

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.

Actual numbers from entertainment industry lawyers and lobbyists form the basis for this, frankly, unbelievable talk about Copyright Math(TM).

http://www.ted.com/talks/rob_reid_the_8_billion_ipod.html

While this talk may seem amusing, the figures he quotes are used to justify all sorts of real world implications for you and I. The Copyright (Infringing File Sharing) Amendment Act came into power last year, the US Embassy attempted to write Section 92A for New Zealand, and now new trade agreements are being negotiated.

Next time you see unbelievable claims, specifically of a numerical nature, question the figures.

And remember to insure your music collection. It’s worth billions.

Thank you for all the suggestions for Stats Crimes (feel free to continue to add your thoughts there too).

We thought you might be interested in a little insight into what the Department of Statistics at the University of Auckland came up with as their pet peeve Stats Crimes during their annual staff retreat recently.

Here’s just a few of them, I’ll post more soon:

Random vs ‘random’

Talkback radio and others not understanding that their listeners and viewers (audience) are not a random population, however ‘random’ they may be.

Definitions and changing definitions

Defining the “measure” they are talking about e.g. poverty, quality of life, employment data. Not stating that “measures” have changed – i.e. definition or classification. Often changes in definition or classification is part of the reason for an increase e.g. autism.

Not really that amazing

Coincidences are more likely than you think.

Association vs causation

Causal headlines from observational studies. “People who are poor watch too much TV. Get rid of TV no more poor people!” (Made this up.)

Bad graphs

Pie charts should be outlawed as comparison of size (areas) are impossible – should use barcharts. 3D graphs should also be outlawed. Chart junk. Uninformative graphics.

The Herald

More than 25,000 animals including fish have died during research and teaching at the University of Otago since 2009, and the figures are expected to increase significantly when statistics are collated for 2011.

No, really?  Going from a two-year total to a three-year total will result in an increase?

We collect multiple years of data for two main reasons: to compute averages (reducing statistical noise) and to compute differences (to learn about trends). Computing totals across multiple years is rarely helpful.

The Otago Daily Times does a better job: it uses the multiple years of data to give trends

Animal use by different groups in New Zealand has dropped by 29% during a three-year period from a record high of 341,520 recorded in 2008.

and

The number of animals being used for research purposes by universities in 2010 has dropped 43% from a high of 123,739 in 2008.

During the Christmas news-deficiency season there was a story warning people to be careful around all the dangerous holiday accident risks.  Our Stat of the Week award went  to Sonia Pollak, who pointed out that 3040 accidents predicted for Christmas Day was quite a bit lower than the average for other days.

The story has returned in the past tense.  The ACC is reporting 3238 accident claims for Christmas Day (close to what they predicted, about 25% lower than an average day) and $850,000 in claims.  Even assuming that the initial claims relate only to medical treatment, that’s about half of the average daily expenditure  (medical treatment, $512 million/yr, hospital treatment – $199.3 million/yr)

We could prevent accidents and save money by being especially careful on Christmas Day.  But we could probably prevent more accidents and save more money by being especially careful on some other day, such as the anniversary of some significant historical accident.  I suggest June 14.

In a report on a cannabis-growing operation in Hamilton, the Herald gives us both new dodgy numbers and recycled dodgy numbers.

The new numbers (from the police)

• Between 50 and 100 plants
• a mature plant worth about $1000
• If 100 plants were allowed to grow to maturity, conservatively worth $400000 in income.

Simple arithmetical operations on these numbers show them to be not entirely consistent: if you can turn a crop that will at maturity be worth between $50,000 and $100,000 into $400,000 in income, you’re in the wrong business.

The recycled numbers are

A study involving the police and Environmental Science and Research released last month found that levels of THC, the primary psychoactive compound in cannabis, was more than four times stronger than in 1996 when ESR last tested it.

As we pointed out last time this statistic appeared, and will keep pointing out when it gets recycled in the future, what they actually found was that in 2004-2006 the maximum concentration was four times higher than the mean concentration in 1996.