Posts from September 2012 (71)

Stuff’s story about the real costs and potential profits of ‘The Block’-style renovations is an example of something we should see more of.  Except, that ideally, we wouldn’t need the newspapers to do it for us.

Matthew Yglesias, at Slate, has a related complaint about ‘math is hard’ descriptions of national budgets

Sometimes you just know that apparent associations just have to be spurious: the price of tea in China really doesn’t affect NZ violent crime rates, and you’re no more likely to win at lotto if you buy your ticket from a shop that’s sold winning tickets in the past.  There’s no way that one could affect the other.

The Herald has a story on functional foods that’s very similar to one I commented on in May.  Again, before even looking at the claims, how could it be true that the shape of a food was a guide to its function? It would be necessary for God to have set it up that way (and, apparently, without bothering to tell anyone).

Match foods to parts of the body for optimum health benefits:

Also, let’s look at some of the examples

1. Healthy Bones: Bony-looking foods such as rhubarb, rich in vitamin K, and celery, rich in silicon, are both good for bones and healthy joints.

Vitamin K was once suggested as involved in bone health, based on observational studies, but a large randomised trial didn’t find any beneficial effect.  Also, although raw rhubarb has moderately high Vitamin K levels (about half as much as cooked broccoli), cooked rhubarb has much less.

3. Sight for Sore Eyes: Slice a carrot and the round circle will show a likeness to an eye, complete with pupil and iris. They contain beta-carotene and antioxidants, both helpful for eyesight issues.

Parsnips have the same shape (as do many roots), but lack the carotenoids.  Orange/golden kumara and pumpkin, which don’t have the eye shape, do have the carotenoids.  And I’m sure you could think of other body parts with more similarity to the carrot than eyes…

5. Round Fruit: Lemons and grapefruit with limonoids and vitamin C are believed to be helpful in preventing breast cancer.

How about quinces, mangoes, coconuts, and melons, which all have historical and cultural support for looking like breasts (or, if we follow Biblical authority, perhaps venison is the relevant food)

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 21 2012.
• Statistics can be bad, exemplary or fascinating.
• The statistic must be in the NZ media during the period of September 15 – 21 2012 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.

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

Twenty-two people didn’t get murdered last year. Another 576 didn’t get robbed. Some 5300 fewer people were ripped off by fraudsters. Those who say we’re drowning in a crime wave appear not to know reported crime is the lowest it’s been this century.

 A good data-based lead in to a story about community policing in the Herald today. Because crimes are much more obvious than non-crimes (I didn’t get mugged today, and my house wasn’t broken into!), it’s easy to think that crimes are increasing whether they are or not.

Two cautionary notes: we can directly observe crime rates going up or down, but the idea that we can directly observe why this is happening is a powerful cognitive illusion.  It looks as though community policing is working, but there could be other reasons for crime going down (for example, whatever is responsible in the US).  Secondly, my reaction to “those who say we’re drowning in a crime wave” is something along the lines of “Really? Who?”  All I could find on the Google were headlines that say “crime wave” when they just mean “more than one crime.”

I don’t know for sure (though I have my suspicions) whether it’s possible to rigorously demonstrate a temperature trend using data just from New Zealand.  I’m sure it’s not possible to demostrate that mammograms save lives using data just from New Zealand.  Fortunately, there’s no real need to do so in either case.

We’ve mentioned the Berkeley Earth Surface Temperature project before.  The project is run by a physicist and former climate-change skeptic, Richard Muller, and has statistical leadership from the eminent David Brillinger.  They have taken a slightly different approach to temperature analyses: they use all available temperature records and weight them for internal consistency rather than selecting a high-quality subset, and their analyses of relationships between temperature and other factors are purely statistical, not based on climate models.  It makes astonishingly little difference (except that they can get better estimates of statistical uncertainty).

Here are two graphs from their results summary page. (more…)

Stuff has a story about another sex survey, with the lead

It appears almost a given that men’s sexual fantasies will differ from those of women and now there’s a survey to prove it.

The link is to the Huffington Post. There’s another link further down the story to the Armenian Medical Network, which, to be fair, is running almost exactly the original press release, including the typos (the respondents are described as 49.6% mend and 0.4% women).

So what was this survey?  It appears to have been a serious attempt to find stuff out, conducted by psychology researcher at the University of Granada.  It hasn’t been published, which is a bad sign and makes it hard to get details, but the press release implies that it has been accepted for publication.

The survey was conducted by questionnaire, and “A number of provincial ongoing training centers, adult education centers, Granada local library and several University of Granada and Universidad Complutense schools collaborated in this study”.  That suggests it wasn’t a random sample. The extremely equal representation of men and women  suggests perhaps a quota sample — interviewers choosing people to ask, from a set of categories. That’s not ideal, but it’s better than just putting a link out on the internet, as was done by the last sex survey we examined, and as the Spanish researchers are doing for their next study according to the press release.

Anyway, what really attracted my attention when I saw the press release was the title:

The US Preventive Services Taskforce has issued another recommendation against general population cancer screening, this time for ovarian cancer.  Although the USPTF guidelines don’t have regulatory force even in the US, let alone here, they are taken seriously because they are developed by people who, generally speaking, have a clue.

In some ways ovarian cancer is an obvious target for screening: it usually isn’t caught until quite late, and earlier diagnosis could theoretically be helpful in treatment.   The current screening approach in countries where screening is done is fairly sophisticated, using a combination of ultrasound imaging and a blood test for a protein produced by ovarian tumours. Even so, a large randomised trial didn’t show any benefit, and the harm from inevitable false positives was significant, since it takes surgery to follow up suspicious findings from screening.  All that can be done at the moment is to be aware of the symptoms of ovarian cancer and get them checked out. The Listener had a good article last year on the topic.

There are some cancer screening programs that are unquestionably lifesaving, eg, mammograms for breast cancer, smear tests for cervical cancer, colonoscopy for colon cancer, and (although the cost may not be justifiable) CT scans for lung cancer in smokers.  Some others, such as melanoma screening, are plausibly beneficial and unlikely to do much harm. In general, though, population screening of healthy people for uncommon diseases has a high bar to surmount: you have to find people with the disease who are treatable now but wouldn’t be treatable if you just waited.  Even more difficult, you also have to do sufficiently little collateral damage to the people (over 99.9% for ovarian cancer) who don’t currently have the disease.

As part of Google’s mind-reading efforts, they have been working on finding connections between search targets: ‘Knowledge Graph‘, as they call it. The idea is partly to group ambiguous search results so you can choose the ones you meant, and partly to suggest other searches that you might be interested in.

For example, if you search for ‘bacon’, you could mean the 16th Century natural philosopher, the 20th century painter, the cured pig product, or actor Kevin Bacon. At the moment, I get the food as the main set of results, with Knowledge Graph side boxes suggesting the two Francis Bacons.  Kevin doesn’t show up until much further down the list.   In partial recompense, Google is advertising Knowledge Graph by providing a Bacon Number calculator, as the Herald tells us.

An actor’s Bacon Number gives their network distance from Kevin Bacon, where each link is a movie collaboration.  The same idea was had first by the mathematicians, who calculate Erdős numbers based on research collaborations with Paul Erdős. Both Bacon and Erdős are notable for the great diversity of their collaborations, not just the sheer number, so most actors and mathematicians have surprisingly small network distances from them . My Erdős number is 45(Scott, Rao, Vijayan, Erdős), and I’m not even a mathematician. Barack Obama has a Bacon Number of 2, and acting is not what he’s most famous for.   The existence of people like Erdős or Bacon makes a huge difference to the structure of a network of contacts — without them, the network tends to come apart into disconnected chunks. Worldwide connectedness is interesting for acting or mathematics, but it is more important in infectious diseases, where a few people can make a big difference to epidemic size.  There’s a nice (if somewhat old) description of some of the research on small-world networks in a magazine from the Santa Fe Institute (in the centerfold)

Back to Google again, the Bacon Number calculator is far from perfect, but the point is that, unlike the definitive Oracle of Bacon, Google gets Bacon Numbers as a by-product of a general approach rather than as a special project. Knowledge Graph also has other failures (for example, it persistently gave the wrong photograph for Australian SF author Greg Egan), but it’s another illustration of Google’s original discovery that links between pages, rather than the contents of the pages, tell you what is important.

[update: I hadn’t realised that my Erdős number decreased from 5 to 4 a few months ago]

Team Ratings for Finals Week 2

Here are the team ratings prior to Finals Week 2, 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 196 matches played, 119 of which were correctly predicted, a success rate of 60.71%.

Here are the predictions for last week’s games.

Predictions for Finals Week 2

Here are the predictions for Finals Week 2