The latest round in the Republican War on Science is a report prepared for US Representative Joe Barton aimed at discrediting the ‘hockey stick’ analysis of global temperatures first undertaken by Mann, Bradley, and Hughes, and subsequently supported by many other studies. For reasons that aren’t entirely clear, this peripheral issue in the analysis of climate change has attracted disproportionate attention from denialists, most notably Ross McKitrick and Steve McIntyre. One result was that the US National Academy of Sciences recently reviewed the work, reaching conclusions broadly supportive of MBH.
The report for Barton was prepared by three statisticians, Edward Wegman, David Scott and Yasmin Said , and its only novel contribution is a social network analysis, which is meant to show that the various independent studies aren’t really independent and that peer review has broken down, since the same group of interlinked academics is reviewing each others’ papers.
Kieran Healy and Eszter Hargittai at Crooked Timber are experts on this stuff, and I’ll be interested to see what they have to say. But in the meantime, I have a couple of observations (feel free to correct errors in my interpretation).
Two network analyses are presented, of which most weight is placed on the first, consisting of a database of 43 individuals. The conclusions reported by Wegman, Scott and Said are as follows:
The block (cluster) structure is very clear. Michael Mann is a co-author with every one of the other 42. The black squares on the diagonal indicate that the investigators work closely within their group, but not so extensively outside of their group. The occasional off diagonal boxes indicate that some investigators have joint papers with investigators outside of their immediate group. The order of the authors on the vertical and horizontal axes is the same. Unfortunately, there is overprinting on the horizontal so that individual authors are not readable. However, it is immediately clear that the Mann, Rutherford, Jones, Osborn, Briffa, Bradley and Hughes form a clique, each interacting with all of the others. A clique is a fully connected subgraph, meaning everyone in the clique interacts with every one else in the clique.
The group of 43 is described as follows
The first specifically focusing on Dr. Mann was developed by first considering all of his co-authors and then examining the abstracts produced by the co-authors. We focus on Dr. Mann because he is the lead author of MBH98/99 and because he is extremely influential in this area as can be seen by his high degree of centrality.
In other words, if I understand things correctly, the first key finding is that (drumroll) Mann has co-authored a paper with every one of his co-authors This obviously demonstrates his “centrality” to the group consisting of his co-authors.
The finding that “Mann, Rutherford, Jones, Osborn, Briffa, Bradley and Hughes form a clique, each interacting with all of the others” can be verified using Google. All those listed were among the authors of:
Mann, M.E., Ammann, C.M., Bradley, R.S., Briffa, K.R., Crowley, T.J., Hughes, M.K., Jones, P.D., Oppenheimer, M., Osborn, T.J., Overpeck, J.T., Rutherford, S., Trenberth, K.E., Wigley, T.M.L., On Past Temperatures and Anomalous Late 20th Century Warmth,Eos, 84, 256-258, 2003.
This automatically qualifies them as a “clique”. So the second finding can be rephrased as (another drumroll) Some of Mann’s papers have lots of co-authors BTW, it appears that Wegman, Scott and Said didn’t catch all the co-authors.
The second analysis uses the 75 most published authors in the field (a much more reasonable choice) and comes to the conclusion
There are some interesting features. Although Michael Mann remains an author with high centrality, Tett, Briffa and Cook emerge as belonging to their own cluster and they also exhibit high centrality. Schweingruber and Collins also appear to have relatively high centrality. One interesting observation is that although Tett is fairly central, he has no direct linkage to Mann. Similarly the Gareth Jones-Allen-Parker- Davies-Stott clique also has no direct linkage to Mann. There are two Joneses. Gareth Jones is not the same person as the person previously labeled as Jones.
My summary (no drumroll this time). There are several leading research groups in this field. Some of them are fairly closely linked to Mann and his group and others are not.