Posts filed under Politics (194)

As you will have heard, excises on smoking are going up.  This will raise money (to the extent that smokers don’t quit) and reduce smoking (to the extent that they do quit).   If you’re interested in the modelling used to estimate the impact on these conflicting goals, the Treasury’s Regulatory Impact Statement is a well-written and detailed explanation.

It’s also interesting to note that Treasury agrees the excise costs are already probably higher than the costs to other people imposed by smoking, and since the smoking excise is probably a regressive tax, the only convincing motivation for smoking excise taxes is to stop people smoking and so improve population health in the long term.

In this light it’s interesting that the Herald’s bogus poll for today is on whether increasing costs will lead to fewer smokers: at the moment, only 11% of responders think it will.  Fortunately, there is strong evidence that the poll respondents are wrong.

There were two Stat-of-the-Week nominations (from Patricia de Guzman and Samantha Post) for the Conservative Party’s use of the Durex Sex Survey to oppose providing subsidised contraception.  We’ve seen this survey number before on StatsChat and it was in the NZ media when the figures were released, back in 2007.

What’s really striking about many of  the stories is the focus specifically on promiscuity of women, when the number that the survey was claiming to estimate is the same for heterosexual men and heterosexual women as a simple matter of arithmetic. 

As is so often the case, the political position seems to be developed independently and statistics sought to drape around it.  Or as Andrew Lang put it  they “use statistics as a drunken man uses lamp-posts — for support rather than for illumination.”

This week, John Key announced a package of mental-health funding, including some new treatment initiatives.  For example, Whanau Ora will be piloting a whanau-based approach, initially on 40 Maori and Pacific young people.

It’s a pity that the opportunity wasn’t taken to get reliable evidence of whether the new approaches are beneficial, and by how much.  For example, there must be a lot more than 40 Maori and Pacific youth who could potentially benefit from Whanau Ora’s approach, if it is indeed better.  Rather than picking the 40 test patients by hand from the many potential participants, a lottery system would ensure that the 40 were initially comparable to those receiving the current treatment strategies.  If the youth in whanau-based care did better we would then know for sure that the approach worked, and could compare its cost and effectiveness, and decide how far to expand it.   Without a random allocation, we won’t ever be sure, and it will be a lot easier for future government cuts to remove expensive but genuinely useful programs, and leave ones that are cheaper but don’t actually work.

In some cases it’s hard to argue for randomisation, because it seems better at least to try to treat everyone.  But if we can’t treat everyone and have to ration a new treatment approach in some way, a fair and random selection is no worse than other rationing approaches and has the enormous benefit of telling us whether the treatment works.

Admittedly, statisticians are just as bad as everyone else on this issue.   As Andrew Gelman points out in the American Statistical Association’s magazine “Chance”, when we have good ideas about teaching we typically just start using them on an ad hoc selection of courses. We have, over fifty years, convinced the medical community that it is possible, and therefore important, to know whether things really work.  It would be nice if the idea spread a bit further.

Last week, The Australian reported on the politics of same-sex marriage in the West Island.  The story is a bit old (I picked it up from John Quiggin), but it’s such an impressive example that it’s still worth mentioning.

Roy Morgan Single Source survey data from the middle of last year shows that over a quarter of Australians aged 14 and over — 26.8 per cent — agreed with the blunt proposition “I believe homosexuality is immoral”.

That’s a fairly small minority, and although there is variation, it’s a minority everywhere in the country. But there is this:

In 80 of the 150 federal electorates, an above-average number of people support the proposition. 

So. In about half the electorates the proportion supporting the proposition is  above the national average (but still a minority), and in about half it is below the national average. That sure tells us a lot.

Thirty-three of these 80 are Labor seats. They take in a who’s who of the ALP.

Of the half that are above the national average, the proportion held by Labor is 41%, a little less than the 48% of all seats they hold.

Nate Silver, at the fivethirtyeight blog at the New York Times, writes

On Saturday, a survey came out showing Mitt Romney with a large, 21-point lead in South Carolina. The poll is something of an outlier relative to other recent polls of the state, all of which show Mr. Romney ahead, but by margins ranging from 2 to 9 points.

The poll, conducted by Ipsos for Reuters, has already attracted more than 200 citations in the mainstream media. Most of these articles, however, neglected to mention a key detail: in a break with Ipsos’ typical methodology, the survey was conducted online….

He goes on to give a good description of the problems with online polling and how the results match up to other techniques in election polls, where there is good evidence of comparability.  These online polls aren’t the `unscientific’ (aka ‘bogus’ web page surveys) we’ve complained about before, they are from polling companies who are at least trying to look accurate.

What Nate Silver doesn’t discuss further is the very large media coverage received by the anomalous poll. If you want election nerds to take you seriously it helps to get the same results as the other polls, but if you want to be newsworthy, it’s better to get very different results.  And since Mr Romney is highly likely to win the presidential nomination, an error that overestimates his popularity will be forgotten in the long run.

Hugo Chavez, the President of Venezuela, has publicly speculated that some secret US weapon might be responsible for several Latin American heads of government getting cancer recently, which he said was “difficult to explain using the law of probabilities.” This is a perfect example of a phenomenon that is all too familiar to public-health workers: the cancer cluster. According to the American Cancer Society, more than 1000 cancer clusters are reported to state public-health departments in the US each year. How many of them turn out to be real? Approximately none.

There are two statistical phenomena here. Firstly, although individual cancer subtypes may be rare, cancer as whole is more common than most people realize. Secondly, we are very good at seeing patterns, even patterns that aren’t there.

The picture, from David Spiegelhalter, shows four 9×9 squares. Three are coloured entirely at random; one has a pattern. Before going on, decide which one you think is non-random.

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Now that the election is over and the question is less urgently political, it might be safe to ask why the NZ media is so fixated on Australia.

NZ net emigration figures for  November have just been released and widely reported on.  At least, net emigration to Australia has been widely reported on.  Total net emigration last month (50 people) hasn’t made the news anywhere except New York.

I’m sure I’m not the only person moving to NZ from somewhere other than Australia who wonders why we don’t count.

I’ve posted this over on Throng as well, but thought I’d add it here too:

I just saw this graph on TVNZ’s election coverage:

Putting aside the issue of using a perspective graph makes it harder to compare, there’s something wrong with this graph: the informal votes (labelled INF) bar is not correct.

The correct graph should look like this:

Update: there are faint notches in their graphic indicating the “0” mark, however it’s not a clear enough distinction.

David Farrar of Kiwi Blog criticises a story in the Herald which says:

John Banks has some support in the wealthy suburb of Remuera, but is less popular on the liberal fringes of the Epsom electorate, according to a Herald street survey.

A poll of 47 Epsom voters yesterday found the National candidate ahead of Act’s Mr Banks by 22 votes to 20.

Farrar correctly points out that the poll is in no way random (i.e. is not scientific), and goes on to say:

But even if you overlook the fact it is a street poll, the sample size is ridiculously low. The margin of error is 14.7%! I generally regard 300 as the minimum acceptable for an electorate poll. That gives a 5.8% margin of error. A sample of 47 is close to useless.

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!”.