According to a P x S x E perspective, the target population for intervention can be identified by who has the problem (P), who interacts with subjects or who is available to provide intervention (S), or the environmental focus of behavior change (E). Targeting a special population for intervention requires that a special need for prevention be demonstrated in that population relative to other populations in terms of especially high levels of drug use, high levels of risk for later drug use, or low levels of exposure to other preventive interventions (an underserved population). In reality, an especially needy population targeted for prevention probably will represent an adverse additive combination or interaction of P, S, and E factors rather than adverse levels on a single factor.
Identifying Target Populations by Person Factors (P)
Findings from etiological and epidemiological research are useful in targeting special populations for intervention based on who has the problem. Currently, this research suggests that high-risk groups can be identified on the basis of several personal behavioral and social factors aside from previous self use, including perceived parent use, perceived peer use, perceived social norms for use, perceived approval or Jack of disapproval of use by family members and peers, personal availability of and access to drugs, early childhood aggressive or antisocial behav- ior, predelinquent or delinquent behavior, low or negative social and academic expectations, and positive expectations about drug use, par- ticularly alcohol use (Newcomb and Bentler 1988; Jessor and Jessor
1977; Hawkins et al. 1988; Kellam et al. 1990; Christiansen and Goldman 1983; Hansen et al. 1987). Identification of high risk on the basis of demographic factors, especially minority status, urbanicity, and socioeconomic status (SES), is less clear than previously believed (Johnson et al. 1990). As noted earlier, drug use prevalence rates for black youth are far lower than rates for white youth, contrary to previ- ous beliefs; however, rates of use among Hispanic youth appear to be increasing at a faster rate than those for either whites or blacks for
some substances (Johnston et al. 1989). Urbanicity and SES
differences are drug specific, although some recent studies suggest an overall increase in drug use in poor rural communities (Oetting et al.
1991). Risk identification on the basis of clinical research on familial and genetic factors is even less clear. Most representative of research
in this area are studies of children of alcoholics. In contrast to animal model studies that have shown a consistent genetic component to alco- holism, only half of the published studies on humans have shown a significant relationship between parental alcoholism and child predis- position toward alcohol or other drug use; the other half show no relationship (Chassin et al. 1988). Finally, with the exception of
indirect evidence from analyses of school dropouts, there has been no research reported on person-level risk for drug use based on under- served or underexposed program status. School dropouts consistently have shown higher rates of drug use compared to school-attending peers, although presumed lack of exposure to school-based prevention programs may be only one of several factors contributing to higher drug use rates in this population (Hansen et al. 1985). Collectively, these research findings suggest that a clearer rationale for identifying target populations based on P factors might be developed relevant to prior drug use, perceptions related to use, expectations, and history of problem behaviors.
Identifying Target Populations by Situation Factors (S)
Findings from psychosocial and survey research are useful in iden- tifying target populations by interpersonal situations or individuals with whom youth interact. In addition to perceived use by others, actual drug use by parents and other adults, peers, and siblings is associated with higher rates of drug use in youth, as are the lack of supportive parent-child communication and the frequency of drug use offers (Hansen et al. 1987; Johnson et al. 1988; Pentz et al. 1989). Risk transmission associated with these variables is assumed to be through interpersonal communication and exposure. An entirely different approach to identifying target populations by situation-level factors is to target individuals or situations that represent opportunities or resources for program delivery. For example, in cities where cross- district or cross-community busing is in effect, it may be difficult to implement a communications-based drug prevention program for parents in a youth’s school. However, if a high proportion of parents
gather in a local community service setting regularly, that setting might be a target for intervention. This was the case in urban Kansas City schools in the Midwestern Prevention Project in which a large pro- portion of inner urban African-American parents could be targeted for a parent preventive intervention through the churches they attended rather than the schools to which their children were bused. Project staff provided training with prevention announcements and messages disseminated through ministers (Pentz 1990). The efficacy of using situational opportunities for identifying target populations for inter- vention versus situational risks has not been evaluated. Findings thus far would support the latter, with some consideration of the ecological validity provided by attention to the former.
Identifying Target Populations by Environment Factors (E)
Focusing on the environmental unit of behavioral change is an additional approach to identifying target populations for intervention. Ideally, the unit of change should match the unit of experimental assignment, intervention, and analysis (Barcikowski 1981; Dwyer et al.
1989). It also should represent the locus of the major drug use problem, although thus far prevention studies have identified units according to convenience, level of program implementation, or hypoth- esized mediators of change (e.g., school as a unit based on program delivery to all students in a school and perceived school-level social norms as a hypothesized mediator of change (MacKinnon et al. 1991). In drug abuse prevention research, logical environmental units of change to consider include, but are not limited to, the following. The individual is the focus of change if changing intrapersonal drug use risk in one-on-one or small group interventions is sufficient to change the individual’s drug use behavior without changing other factors. The group is the identified target if peer pressure or group norms for drug use constitute the major problem and if changing these factors in a small-group setting produces a change in group drug use. The school is the target if such factors as low teacher morale for teaching, poor school administration, or the lack of school monitoring of on-campus drug use constitute the major problems contributing to drug use and if changing the school environment by including all students and school staff in intervention produces a change in school-level drug use. The community is the target for intervention if community supply and demand for drug use, drug-related crime rates, and perceived social
norms for and acceptance of drug use are high and if use of multiple community channels for program delivery and changing local drug use policy are likely to change community-level drug use. Current re- search on primary and secondary drug prevention programs suggests that, with social influences constituting the major risk factors for drug use onset and progression to regular use in youth, targeting social units for intervention rather than individuals may have a higher likelihood of changing drug use.
An illustration of the use of P, S, and E factors in identifying target