Commentary on: “Indicators of European public research in hydrogen and fuel cells—an input–output analysis”

The output of European public research in hydrogen and fuel cells in terms of number of publications is reported in the paper by Seymour et al. [Indicators of European public research in hydrogen and fuel cells—An input–output analysis. Int J Hydrogen Energy 2007; 32(15): 3212–22]. The counting method for publications is not stated but whole counting has been used. It is not mentioned that the rankings of different countries might have changed if other counting methods had been used. The paper also reports measurements of citations based on the publications counted. The difference in results obtained by using different counting methods will be larger for citations but this is not mentioned. The values for the number of publications for the European countries have been added to provide the value for EU + . However, values obtained by whole counting for individual countries cannot be added to provide correct values for a union of these countries. Therefore the comparison reported in the paper between the publication output for EU + and for US, Japan and China is invalid.