a survey of drug use , carried out in 1981 by means of a self-reported anonymous questionnaire administered to a stratified probability sample of 4,306 school students in grades 5 , 7 , 9 , 11 and 13 in ontario , canada , found consistent patterns in the use of drugs , including infrequently used illegal drugs such as heroin .
C0029040
ontario
C0006823
canada