Smoking habits, alcohol consumption and the use of drugs by schoolchildren from the age of ten / frequency of absence, truancy / having a payed job, earnings allowance / knowledge of hashish and marihuana / use of alcohol, tobacco, amphetamines, sedatives, marihuana, hashish, cocaine, heroine, glue etc. / frequency and quantity of use, now and in past / reaction of parents / use of alcohol, tobacco and drugs by friends / obtainability of alcohol and drugs. Background variables: basic characteristics/ place of birth/ residence/ occupation/employment/ education/ religio