An unpublished statistics book - tom's webpage

If those data were for a true experiment based upon a non-random sample, there are "9 choose 4" (the number of combinations of 9 things taken 4 at a time) = 126 randomizations that yield Pe 's ranging from 0.00 (all four 0's in Group 1) to 80 (four 1's in Group 1 and only one 1 in Group 2). ................
................