Suppose one of the variables is “owns yacht” (yes/no). If both records have a “1,” indicating they both own a yacht, this is a strong similarity. However, if both have a “0,” this does not tell us much, since nearly everyone is a “0.”
Jaquard?s coefficient is
Where d is the number of 1/1 agreements, and b and c are the 1/0 and 0/1 disagreements. Thus, it is the number of meaningful agreements divided by the meaningful agreements+ disagreements.