In the treatment of heroin addiction by methadone hydrochloride maintenance, it is customary to test urine specimens regularly, in order to monitor each patient's illicit use of drugs and to assess the general success of the program. Principles and graphs are presented here to aid the physician in choosing an economical testing frequency, and in interpreting the results quantitatively on a correct statistical basis. For most purposes, a random testing schedule at an average frequency of once in five days will suffice.
Goldstein A, Brown BW. Urine Testing Schedules in Methadone Maintenance Treatment of Heroin Addiction. JAMA. 1970;214(2):311-315. doi:10.1001/jama.1970.03180020031006