Today I was looking into my citation profile. And when I checked self-citation, I noticed a Nature article that baldly claimed “Men cite themselves more than women do…The apparent trend has been on the rise over the past two decades.” They not only almost interpret it as a causal relation, but also goes further and suggest “it is something that hiring and tenure committees should take into account when assessing the impact of researchers and their work”.

Well, the method of this research is simply to count the citation in each group, and compute the self citation rate. But the claim is hardly anything causal. Assuming a person cites all his previous publications at each new paper. When he has $N$ publications, he would have $1+2+ \dots + (N-1) = O(N^2)$ self citation, making his self citation rate O(N). In realty this cannot happen as when N=100, one cannot really cite 100 previous publications so probably the self citation rate goes $O(N^d)$ for some $0<d<1$. In short, the total number of publication is such as huge confounder that any conclusion is unlikely sensible without taking into this factor into account.

The booming literature on these research citations reminds me of a story that the 20-th century Chinese novelist Luxun told in his biography: he used to be a student in a mining school where the students run a experimental colliery. But the production of that colliery was so low that it was merely sufficient to feed the power generator of the pump used for mining.