Measuring the drug use of the residents of a city has always been difficult. In the past, current drug use was estimated from questionnaire responses, but due to the social stigma associated with drug use, a large amount of response bias was known to be present. A proposed method for measuring a city's current drug is to measure the amount of drugs detected in the inflow to the city's wastewater treatment facility. This method was used to compare the Marijuana usage, through the measurement of the active ingredient THC-COOH, of London versus Milan over a 3 week period. Samples were made at randomly chosen times throughout the day for 21 consecutive days in both cities. Units are mg/day/1,000 people. What are the two independent samples