Posts written by Thomas Lumley (2645)

Housing prices are in the news again, and I was curious to see how much of the change in prices is just ordinary inflation, and how much is real improvement. Over the past 45 years, housing prices have increased more than fifty-fold.  Barfoot & Thompson like to point this out, and they have a graph of Auckland prices that is designed to show the increase very dramatically.  But other things from apples to yachts are also more expensive than they were in the past. (more…)

Q: Did you see the BBC news article about dietary fibre and bowel cancer?

A: No, but I’ll go look. [reading noises]

Q: Well?

A: They definitely  get points for linking to the article in the British Medical Journal (and it’s even an open access article that anyone can read).

Q: Haven’t we beaten that issue into the ground yet?

A: Apparently not. (more…)

Stuff is reporting, in their Oddstuff section, a story about twins who will turn 11 tomorrow, 11-11-11.  How odd is this?

There are about 64000 births per year in New Zealand, or about 175 per day.  The rate of twin births is somewhere between 1 in 60 and 1 in 100, so on an average day, such as 11-11-00, there will be about two pairs of twins born.  So we’d expect two pairs of Kiwi twins to turn 11 on 11-11-11. You might wonder what the other pair was doing.

If you read the story, though, you see it’s actually from the United States: Madison, Wisconsin.  There were more than 50,000 pairs of  twins born in the US in 2000, so we’d expect about 136 pairs turning 11 tomorrow.

There must be lots of community papers across the world reporting on a pair of local twins turning 11 tomorrow.  The interesting question  is how the Overman twins got their story on to the Associated Press wire and into 181 (and counting) newspapers around the world, and how the same mechanisms are used on stories that aren’t just harmless fluff.

Updated:  Now there’s a local pair of twins, one of  whom is quoted as saying “There are probably only one or two [sets of twins] in the world turning 11 on that date.” 

Updated again: You’d expect there to be several sets of birthday triplets out there somewhere in the industrialized world, and one set have shown up in Windsor (Canada). Unfortunately, the story also spends a lot of time with Uri Geller, trying to get Deep Significance out of the date.

It’s a familiar phenomenon that a party leader can be more popular, or less popular, than the party they represent. For example, Labour is currently more popular than Phil Goff.

The problem is especially difficult to handle in the US elections. At the moment, we pretty much know that Barack Obama will be the Democrats’ presidential candidate next year.  We don’t know who the Republicans will pick.  You could run a poll asking “Would you vote for Obama or for a Republican opponent”, or you could pick one of the current candidates for the Republican nomination and ask “Obama vs Cain” or “Obama vs Romney”.  It turns out to matter.

In the current polls, President Obama loses to Generic Republic Opponent by about 3%, but beats everyone in the current Republican field. The only actual Republican who comes close in current support to Fill In The Blank is Mitt Romney, who is about 2% behind Obama.    We’ll have to wait until February to see what happens when the Republican nominee is chosen.

As you may remember, there was a flurry of headlines recently in the Kiwi media about the new anti-clotting drug dabigatran(Pradaxa) — it’s not often than Pharmac is accused of pushing too hard for an expensive new substitute instead of  an old, cheap drug.  Now, in Australia, the reverse is happening: the Goverment has refused to list dabigatran for subsidy (going against its own experts), and the media is reporting this decision as a danger to Australian patients (with help from the manufacturer’s lobbyists).

Warfarin (yes, rat poison) is a very safe and effective anti-clotting drug if it’s given at exactly the right dose. Unfortunately, the right dose varies between people, and changes depending on almost anything else (food, medications, herbals, alcohol) you might consume.  Keeping the dose right requires frequent blood tests, which are inconvenient and expensive, and even then the dosing is often imperfect unless you and your physician are truly obsessive.  But there hasn’t been anything else that came close to the safety and efficacy of warfarin.

Now there is a rush of new medications coming out that selectively disrupt a very late stage in clot formation: as well as dabigatran there are apixaban, rivaroxaban, and betrixaban.  These don’t have the variable dosage of warfarin, so it should be possible to just prescribe them and stop worrying: a big improvement in convenience and saving in cost.  On the other hand, these drugs are new (and so less well understood), and unlike warfarin there is no antidote and no convenient lab test for overdose.  And they are quite  expensive, even with Pharmac’s well-known haggling powers.

In this case I think the evil multinational drug company is right and the Australian Health Minister is wrong: these new drugs really are safer and more effective — they were better than warfarin in a large randomized trial, where warfarin dosing is likely to be better than in free-range patients — and the reduced need for blood tests will pay for quite a bit of the increased cost.  Still, it’s hard to avoid the suspicion that the main urgency in this debate is to get dabigatran into widespread use before its competitors make it on to the market…

Stuff is reporting on this year’s “Global Gender Gap Report” from the World Economic Forum.  New Zealand has improved very slightly over last year in its gender equality score, but has lost 5th place in the rankings to Ireland, which had greater improvement. The biggest improver was Yemen, whose situation went from dire to merely awful, though it is still last. Colombia, Nepal, and Sri Lanka had the biggest falls.

One thing Stuff did get wrong: the rankings are based on a complicated “gender gap score”, not just on pay equity.  New Zealand still does slightly better on pay equity than Ireland, but Ireland does better on having women in senior positions.

There are many ways that sophisticated pollsters can tilt the result of a survey: biased samples, carefully framed sets of questions, creative subsets of the data.

Based on a survey of protesters at Occupy Wall Street, pollster Doug Schoen wrote ” it comprises an unrepresentative segment of the electorate that believes in radical redistribution of wealth, civil disobedience and, in some instances, violence. . . .”.

The actual data from that very survey:

What would you like to see the Occupy Wall Street movement achieve? {Open Ended}
35% Influence the Democratic Party the way the Tea Party has influenced the GOP
4% Radical redistribution of wealth
5% Overhaul of tax system: replace income tax with flat tax
7% Direct Democracy
9% Engage & mobilize Progressives
9% Promote a national conversation
11% Break the two-party duopoly
4% Dissolution of our representative democracy/capitalist system
4% Single payer health care
4% Pull out of Afghanistan immediately
8% Not sure

Andrew Gelman says about this poll “as I like to remind students, the simplest way to lie with statistics is to just lie!”. 

The Berkeley Earth Surface Temperature project has just released its first data sets and analyses.  The aim of this project is to summarise all the temperature records around the world in a comprehensive and transparent way, both to get an estimate of changes in global temperature and to make it easy to see the impact of  data quality filters that have been applied by previous climate modelling projects.  So far, they have analysed all the land measurements; ocean measurements are coming next. You can download the data and code yourself, and check their findings or explore further (if you actually want 1.6 billion temperature measurements — don’t try this on a smartphone).

The main finding of the project won’t surprise most people: it’s getting hotter. More importantly, the estimates based on all available data agree almost perfectly with the previous estimates that were based on a small subset of ‘best’ weather stations.  Incorporating lower-quality stations doesn’t change the estimates. Even using just the low quality stations gives pretty much the same estimates. Other things that don’t affect the results include the urban heat island effect: cities are hotter than the countryside, but most of the world isn’t in a city. They’ve also made a neat movie of the climate since 1800: you can see the normal oscillations over time, and the heating trend that eventually swamps them.

Combining temperature records with varying quality, measurement frequency, and duration, is a major statistical task even without considering the volume of data involved. The statistical expertise on the Berkeley Earth team includes an Auckland Stats graduate (and Berkeley Stats PhD), Charlotte Wickham.

Updated to add: this is now in the Kiwi media: NZ Herald, Stuff, 3 News.

What’s the best strategy if you want to have a perfect record betting on the rugby?  Just bet once: that gives you a 50:50 chance.

After national statistics on colorectal cancer were released in Britain, the charity Beating Bowel Cancer pointed out that there was a three-fold variation across local government areas in the death rate.  They claimed that over 5,000 lives per year could be saved, presumably by adopting whatever practices were responsible for the lowest rates. Unfortunately, as UK blogger ‘plumbum’ noticed, the only distinctive factor about the lowest rates is shared by most of the highest rates: a small population, leading to large random variation.

 His article was picked up by a number of other blogs interested in medicine and statistics, and Cambridge University professor David Speigelhalter suggested a funnel plot as a way of displaying the information.

A funnel plot has rates on the vertical axis and population size (or some other measure of information) on the horizontal axis, with the ‘funnel’ lines showing what level of variation would be expected just by chance.

The funnel plot (click to embiggen) makes clear what the tables and press releases do not: almost all districts fall inside the funnel, and vary only as much as would be expected by chance. There is just one clear exception: Glasgow City has a substantially higher rate, not explainable by chance.

Distinguishing random variation from real differences is critical if you want to understand cancer and alleviate the suffering it causes to victims and their families.  Looking at the districts with the lowest death rates isn’t going to help, because there is nothing very special about them, but understanding what is different about Glasgow could be valuable both to the Glaswegians and to everyone else in Britain and even in the rest of the world.

Q:  So what’s with this green tea article at Stuff.co.nz?

A: It’s reporting an experimental study on weight loss using green tea extracts

Q: And did it work?

A: Yes, the treated subjects gained less weight than the untreated ones, by about 4g. (more…)