Saturday, June 11, 2011

Global Warming is Now Statistically Significant! Should We Care?

The BBC reports that global warming has passed an arbitrary (though conventional) threshold of statistical significance. From the article:
By widespread convention, scientists use a minimum threshold of 95% to assess whether a trend is likely to be down to an underlying cause, rather than emerging by chance.

If a trend meets the 95% threshold, it basically means that the odds of it being down to chance are less than one in 20.

Last year's analysis, which went to 2009, did not reach this threshold; but adding data for 2010 takes it over the line.

"The trend over the period 1995-2009 was significant at the 90% level, but wasn't significant at the standard 95% level that people use," Professor Jones told BBC News.

"Basically what's changed is one more year [of data]. That period 1995-2009 was just 15 years - and because of the uncertainty in estimating trends over short periods, an extra year has made that trend significant at the 95% level which is the traditional threshold that statisticians have used for many years.

I agree with Andrew Gelman's response here. Overall this is a pretty good example of why fixating on statistical significance is often weird and distracts from the importance of the core analysis, which in this case is pretty important.

(via Andrew Gelman)
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