A clinical psychologist has developed a technique to help obsessive-compulsive disorder clients avoid intrusive and disturbing thoughts, and wants to know if this technique is really effective. She asked 10 OCD clients to try the technique for two hours and recorded the number of times that they experienced an intrusive thought during that time period. Their data are as follows:
7, 12, 11, 11, 12, 12, 4, 7, 9, 5
What is the mean of this distribution?
a) 9
b) 10
c) 12
d) 7