Google Scholar Metrics: an unreliable tool for assessing scientific journals

We introduce Google Scholar Metrics (GSM), a new bibliometric product of Google that aims at providing the H-index for scientific journals and other information sources. We conduct a critical review of GSM showing its main characteristics and possibilities as a tool for scientific evaluation. We discuss its coverage along with the inclusion of repositories, bibliographic control, and its options for browsing and searching. We conclude that, despite Google Scholar's value as a source for scientific assessment, GSM is an immature product with many shortcomings, and therefore we advise against its use for evaluation purposes. However, the improvement of these shortcomings would place GSM as a serious competitor to the other existing products for evaluating scientific journals.