Many thanks to Lutz Bornmann for making me aware of these highly relevant references which I only became aware of after publication of this article:
1. Bornmann, L., Mutz, R., Daniel, H.-D., Wallon, G., & Ledin, A. (2009). Are there really two types of h index variants? A validation study by using molecular life sciences data. Research Evaluation, 18(3).
2. Bornmann, L., Mutz, R., & Daniel, H.-D. (2009). Do we need the h-index and its variants besides standard bibliometric measures? Journal of the American Society for Information Science and Technology, 60(6), 1286-1289.
3. Bornmann, L., Mutz, R., & Daniel, H.-D. (2008). Are there better indices for evaluation purposes than the h index? A comparison of nine different variants of the h index using data from biomedicine. Journal of the American Society for Information Science and Technology, 59(5), 830-837.
