Statistical reliability of citation frequency as an indicator of scientific impact

The article deals with the statistical problem of the difference between the mean citation frequencies of two sets of papers required to be significantly different. An analysis of citation data indicated that, as a first-order approximation, (1) The relative spread due to a short observation interval is independent of the long-term citation frequency and (2) the relative spread in long-term citation frequencies of different papers from the same author is independent of the mean citation score for the papers by that author. As a rule-of-thumb, these two sources of variance can be characterized by standard deviations of a ratio (factor) of 2 and 3, respectively. By applying these results to citation data published in the literature, it is shown that sometimes statistically unjustified conclusions have been drawn in the past.