title: Computing degree of similarity among a group of sets
body: <p>Suppose there are 4 sets:</p>
  
  <p>s1={1,2,3,4};<br>
  s2={2,3,4};<br>
  s3={2,3,4,5};<br>
  s4={1,3,4,5};</p>
  
  <p>Is there any standard metric to present the similarity degree of this group of 4 sets?</p>
  
  <p>Thank you for the suggestion of Jaccard method. However, it seems pairwise. 
  How can I compute the similarity degree of the whole group of sets?</p>