California State Assembly Bill 2071 (AB 2071) mandated that patients at methadone clinics be required to undergo a minimum of 50 minutes of counseling per month. Evan Kletter (A-32)

collected data on 168 subjects who were continuously active in treatment through the Bay Area Addiction Research and Treatment (BAART) centers for 1 year prior to, and 2 years after AB 2071’s implementation. Prior to AB 2071, BAART center counselors spent two sessions of at least 15 minutes per session per month with each client. The subjects in the study were also identified as cocaine abusers. The observations in KLETTER are the percentages of failing a cocaine drug test for each of the subjects pre- and post-AB 2071. For example, a pre-value of 60 implies that the patient failed a cocaine test 60 percent of the time prior to adoption of AB 2071.

Dr. Kletter performed a Wilcoxon rank sum test to determine if the percentage of failed tests decreased significantly after the passage of AB 2071. Use the data to determine what conclusion he was able to reach. Report the test statistic and p value.