<prompt> The best sampling method used for drug abusersQuota samplingSnowball samplingCluster random samplingNone of the above  <response>: Snow-ball SamplingA technique for developing a research sample where existing study subjects recruit future subjects from among their acquaintances; thus the sample group appears to grow like a rolling snowballIs often used in hidden populations which are difficult for researchers to access, e.g. drug users or commercial sex workers. 