Thursday, June 18, 2009

Damned statistics and climate change

A news item in the local Southern Courier discussed the privately-owned train link to Sydney's airport.
  • Botany Bay's Mayor Ron Hoenig: "In reality, it was shown to be cost inefficient, and a disaster."
  • In response, "Airport Link chief executive Tim Anderson... said there had been a 27 per cent increase in patronage on the airport line over the past two years."

The context was the exhorbitant charge for that particular stretch of rail ($14.80 from central, one way), and the effect on locals who might otherwise use it.

Put aside other issues, such as whether the patronage increase justifies the usage charge, or whether the increase was from such a low base that any change would look like a win.

The question is over the use of the statistic, and how it can mislead. If Anderson looked at the fluctuating usage figures over the past 9 years since opening, he could pick any two years he liked to make his point. Likewise, Hoenig could pick any other years to justify the opposite perspective. For a reality check, read about Airport Link above.

As with a work of fiction, most people don't stop to question figures presented in a news report. There's just not enough time in the day to analyse everything.

Climate change skeptics are particularly guilty of this. As this article details, Steve Fielding, a key balance-of-power Senator, was persuaded that there is no significant issue because global temperatures are not significantly different from those of ten years ago.

And that is a favourite approach of climate change skeptics - near universally, they use this trick (eg The Great Climate Change Swindle). Pick a year that was slightly out of kilter with its neighbours (in this case, 1998, which had a strong El Nino weather pattern) to prove the case. Take that statistic in isolation, without revealing or analysing the sequence of readings over time. Which in this case show that the past ten years have been the hottest decade on record.

(An extension of this argument is the use of long-range figures to show that Earth's climate has always been changing, and has indeed been hotter. True, but a) significant evolutionary change - including much species extinction - accompanies such changes), and b) we are currently inducing one of the fastest periods of climate change in the planet's history.)

It's devilishly hard to read statistics with a critical eye, if you don't have access to the full data set. The best that can be done is to scan for context. (In the case of Fielding, he's known as a conservative who is not fiercely intelligent, and he went fact-finding to the US, hosted by the Heartland Institute, known as conservative and funded by fossil fuel and tobacco interests, amongst others.) Scanning for context includes a healthy degree of questioning, critical analysis, and absorbing information from a variety of credible sources. But you knew that already, didn't you?

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