There are many similarity measures (e.g. Jaccard, Sorensen, etc), each of them is sensitive to different properties of the compared sets. I would like to use the metric $S=\frac{N_{A\bigcap B}}{min(N_{A}; N_{B})}$, where $N_{A}$ is the count of set $A$. So basically I divide the size of the intersection by the size of the smaller set. I am sure I am not the first who found this out, and maybe it has some pretty name. Does anybody know?