A surprising number of people are scared of clowns. You expect that people will have more nightmares the night that they see clowns at the circus. To test this, you send a group of people to a circus with clowns, and a group to a circus without clowns, and measure the number of people in each group who have nightmares that night. Your data is shown below: Nightmares Nice dreams
No clowns 12 35
Clowns 30 8
Perform a Z-test on nightmares after the no-clown circus minus nightmares after the clown circus. Report the test statistic.