In journal club last year we read Michaletz et al. (2014) “Convergence of terrestrial plant production across global climate gradients” Nature doi:10.1038/nature13470 along with the critique by Chu et al. (2015) in Global Change Biology.
The paper tests whether Net Primary Production (NPP) is more strongly related to climate or to stand biomass and age, using a dataset of NPP compiled from a number of sources. We found it a bit odd that about 90% of the 1200 entries in the dataset came from just one source – a Chinese PhD thesis from 1996. PhD student Jim Yang downloaded the thesis and translated the relevant bits and we realised that the “data” were not measured at all, but modelled as a function of stand biomass and age. Clearly such “data” cannot be used to test for relationships with biomass and age.
To their credit, Michaletz et al. responded rapidly when we emailed them about this issue (that can’t have been a nice email to receive!) They submitted a correction to Nature in early January and it has finally been published, along with a revised version of their dataset which contains just 138 entries.
The debate over the analysis by Michaletz et al. will no doubt continue (see Chu et al. 2015) but at least it can now do so with a considerably less flawed dataset. A win for journal club!