RT Article T1 Research methods for illegal drug use in hidden populations: summary report of a European invited expert meeting JF Journal of psychoactive drugs VO 26 IS 1 SP 33 OP 40 A1 Goor, L.A.M. van de LA English YR 1994 UL https://krimdok.uni-tuebingen.de/Record/1639441530 K1 Drogenkriminalität K1 Erfassungsmethoden K1 Betäubungsmittelgebrauch