“The Overlap Coefficient is defined as the size of the intersection divided by the smaller of the size of the two sets.”

I think you mean:

“The Overlap Coefficient is defined as the size of the intersection divided by the size of the smaller of the two sets.” ]]>

Also Hamming Distance between finite sets:

http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.224.4799

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