This news article has made a bit of a splash: Seth Borenstein sent around a temperature time series to four statisticians–just sending the numbers without saying where they came from–and the statisticians uniformly concluded that there were no consistent temperature declines over time:
“If you look at the data and sort of cherry-pick a micro-trend within a bigger trend, that technique is particularly suspect,” said John Grego, a professor of statistics at the University of South Carolina.
I don’t have anything to add on the temperature series–there’s only so much you can learn from a context-free data analysis, and I don’t think anyone would want to take this particular set of blind statistical analyses as being at all informative about the science. But there’s more going on here.
This stuff has been in the news when Freakonomics authors Steven Levitt and Stephen Dubner wrote the following:
While the drumbeat of doom has grown louder over the past several years, the average global temperature during that time has in fact decreased.
But then, after the book came out, we hear that “Levitt, a University of Chicago economist, said he does not believe there is a cooling trend.”
And on their blog, Dubner recently seemed to be endorsing the view that future trends are “virtually assuring us of about 30 years of global cooling.”
As I wrote earlier, I don’t think it’s so horrible for Levitt/Dubner to have a mix of partly conflicting attitudes on the topic. Neither Levitt nor Dubner is an expert on climate change, and it’s probably a good thing that their attitudes are fluid and not so easy to pin down. You also get a sense of the confusion that can arise when using vague but seemingly-precise terms such as “decrease,” “trend,” and “virtually assure.”
The other thing that might amuse you is that I was one of the statisticians asked to analyze the dataset! Borenstein sent a request to the American Statistical Association asking for some statisticians to analyze do a trend analysis of a time series but without knowing what the data are about. The ASA sent it to a bunch of members they have on file who are willing to field media requests. I’m on that list. I didn’t join in this one, partly because I’m wary of analyzing data without context (it’s not really what I do) and also because I haven’t done much work on time series. In retrospect, it would’ve been fun to have been part of this but I’m glad I didn’t get involved; it would’ve been complicated, given that I’ve already been writing about Freakonomics from a more general perspective. Also, I’m involved in some research right now on climate time trends, and it would be a bit awkward if I were quoted saying one thing if our research turns up something different.
P.S. Again, my goal here is not to “debunk” Levitt, Dubner, or for that matter Borenstein, but rather to use this as an example of how difficult it can be to pin down the meanings of even very simple statistical terms.