Empirical distribution of citation impact values conditioned on publication number n . We aggregate the normalized citation z values of researcher profiles with first publication year for Nat./PNAS/Sci. and for the economic sciences, and with and . Each panel shows the probability distribution conditioned on publication number . The z-scores represented by each represent a subset of the aggregate set of z values, independent of and . Because the unconditional distribution of z values is approximately normal with mean 0 and with units of the standard deviation (), we also plot a normal distribution in each panel for reference (red curve).