Less than zero

There’s been a bit of publicity about a recent study of the effects of the Australian gun buyback. The central finding of the authors was that, while gun homicides declined after the buyback this was merely a continuation of a pre-existing trend.


I’m dubious about the whole approach. In the absence of a well-founded explanation for the trend, there’s no reason to treat maintenance of the trend, rather than the level, as the null hypothesis. The rate of gun homicides has clearly fallen (the authors find the same for suicides), so the data supports the policy, contrary to the claims.

And eyeballing the data, I’m doubtful that it’s even sufficient to establish the existence of a declining trend for the period up to and including 1996. It might be argued that the Port Arthur massacre in 1996 should be excluded and that a downward trend would then emerge, but, given that this was the even that precipitated the buyback, this seems like begging the question to me.

In any case, Andrew Leigh has the ultimate knockdown objection. If you look at the confidence intervals, the only way the gun buyback could have been shown to work, on the authors’ tests is if gun homicides fell below zero by 2004. Clearly, even if you buy the declining trend story, a linear trend is just wrong.

Mark Bahnisch has more, though quite a few commenters don’t seem to appreciate how conclusive Leigh’s refutation has been.


The Washington Post is having a good day. There’s a nice article by Shankar Vedantam linking the research of Kahneman and Tversky on anchoring heuristics to widespread unwillingness to believe estimates of 600 000 excess deaths arising from the Iraq war.

And the Post which has kowtowed to Bush ever since he got in, finally seems willing to call him on obvious lies. Here’s Peter Baker and Eugene Robinson.

No doubt the collapse of hope regarding Iraq has something to do with us. The US media has finally come face to face with the reality that all the alternatives now on offer are disastrous. Even the hawks have now recognised that the costs of the war have far outweighed any benefits that might be achieved. Unfortunately, this recognition has come a few years too late for the people of Iraq, but there’s at least time for US voters to cast their verdict in November.

What I’ve been reading

Old: Sense and Sensibility. Probably my favourite among Jane Austen’s novels. By the way, has anyone else noticed that while Austen’s heroines are interestingly different, all her books seem to feature the same two male characters – the attractive, but dishonest younger man (Willoughby, Wickham, William Elliot, Frank Churchill) and the seemingly reserved, but really passionate (and usually older) man (Darcy, Brandon, Knightley, Wentworth). I wonder if this is just a handy plot device or whether it reflects some event in Austen’s life, of which we know little.

New Anansi Boys by Neil Gaiman. A great story, and also interesting for the link between Anansi, the West African trickster-spider and Brer Rabbit, which is obvious enough once pointed out (there’s even a tar baby story) but was still new to me.

Exxon: We believe in global warming, so we shouldn’t be criticised for funding global warming denialists

As everyone knows (or ought to know by now), one of main reason controversy over climate change is continuing in the face of overwhelming evidence is the fact that ExxonMobil has the cash spigot open to fund anyone willing to deny the evidence – the Competitive Enterprise Insitute, George Marshall Institute and the old tobacco industry network run by Steven Milloy, Fred Seitz and Fred Singer have been among the main beneficiaries. The Royal Society wrote to them recently, asking them to turn off the money tap.

Exxon’s response

The Royal Society’s letter and public statements to the media inaccurately and unfairly described our company.”

It went on: “We know that carbon emissions are one of the factors that contribute to climate change – we don’t debate or dispute this.”

So, they know the groups they are funding are lying, but they need to promote the idea that there is so much uncertainty that we should do nothing. The best way to do this is to create as much Fear, Uncertainty and Doubt as possible.

Close the freeway for good?

A few days ago, cracks were discovered in the on-ramps to the Riverside Expressway, Brisbane’s main access route to the city. The decision was made to close the ramps and a large section of the freeway immediately and, not surprisingly, chaos ensued. The debacle was used to make the case that we need more freeways, tunnels, bridges and so on.

But three days later, the ramps are still closed and everything is working as smoothly as you could imagine. I took the ferry to Southbank at 8am yesterday to teach a course. It was full, but not overcrowded, and the traffic was zipping over the bridges as if it was Sunday. There’s been a big shift to public transport and people have been avoiding or rescheduling trips into the city. Obviously, the second of these is, in large part, a temporary adjustment that won’t be sustained indefinitely, but quite a few people have discovered that taking the train or bus into town is actually easier than driving.

Looking at this experience, it seems as if having the freeway closed for a while has done us some good. We should try it again some time.