Selective prevention strategies target subsets of the total population that are deemed to be at risk for substance abuse by virtue of their membership to a particular population segment, for example young offenders, school drop-outs, or students who are failing academically. Risk groups may be identified on the basis of social, demographic or environmental risk factors known to be associated with substance abuse, and targeted subgroups may be defined by age, gender, family history, place of residence such as deprived neighbourhoods or those with high drug-use or trafficking.