Excerpt from Nature News
Performance metrics based on values such as citation rates are heavily biased by field, so most measurement experts shy away from interdisciplinary comparisons. The average biochemist, for example, will always score more highly than the average mathematician, because biochemistry attracts more citations.
The new ranking that allows to compare the impact across disciplines appears on the website Scholarometer, developed by Filippo Menczer, an informatician at Indiana University Bloomington, and his colleagues Jasleen Kaur and Filippo Radicchi. It relies on queries made through Google Scholar to normalize the popular metric known as the h-index (a scientist with an h-index of 20 has published at least 20 papers with at least 20 citations each, so the measure takes into account quantity and popularity of research).