Epidemiological data show that substance misuse, antisocial behavior, and health-risking sexual behaviors (HRSBs) are prevalent in emerging adulthood, both in the US–the setting for the PROSPER study–and internationally. For example, in 2014, the US annual prevalence estimates for any illicit drug use were highest among 19–22 year olds (41%; Johnston et al. Reference Johnston, O'Malley, Bachman, Schulenberg and Miech2015a ). Especially noteworthy is the 6.7% annual prevalence estimate of narcotic use, including heroin and non-medical use of prescription opioids, which is higher among young adults (aged 19–26) than any other age group. As an example of the prevalence of HRSBs, in the US approximately 24% of young adults have more than one sex partner annually and 30% of unmarried respondents report never using a condom (Johnston et al. Reference Johnston, O'Malley, Bachman, Schulenberg, Patrick and Miech2015b ). Concerning antisocial behaviors, offending behavior (violence and theft) peaks at around 10–12% between ages 17–19, although it then begins to decline (Piquero et al. Reference Piquero, Farrington and Blumstein2007; Loeber et al. Reference Loeber, Farrington, Stouthamer-Loeber and White2008).

Internationally, surveys of 18–29 year olds in several major countries in Europe, Africa, Asia, and the Americas have been conducted by the World Health Organization and other international agencies. They show pervasive substance misuse among young adults, albeit with a high degree of variability in the drugs of choice across countries. For example, while 44.1% of 22–29 year olds living in France reported that they used cannabis, only 13.7, 1.8, and 1.9% of those living in Italy, China, and Nigeria, respectively, reported such use (Degenhardt et al. Reference Degenhardt, Chiu, Sampson, Kessler, Anthony, Angermeyer, Bruffaerts, de Girolamo, Gureje, Huang, Karam, Kostyuchenko, Lepine, Mora, Neumark, Ormel, Pinto-Meza, Posada-Villa, Stein, Takeshima and Wells2008).

Substance use and associated health-risking behaviors have health, social, and economic consequences, at both the individual and societal levels. These problems can lead to later substance abuse and dependence (Swendsen et al. Reference Swendsen, Conway, Degenhardt, Glantz, Jin, Merikangas, Sampson and Kessler2010); marijuana use has been linked to later addiction, altered brain development, diminished achievement, and ongoing mental health difficulties (Fergusson & Boden, Reference Fergusson and Boden2008; US Department of Justice, Drug Enforcement Administration, 2014; Volkow et al. Reference Volkow, Compton and Weiss2014; Fischer et al. Reference Fischer, Clavarino, Plotnikova and Najman2015; Coffey & Patton, Reference Coffey and Patton2016); alcohol misuse is associated with multiple health-related disease and injury conditions (Rehm, Reference Rehm2011); and deaths from prescription drug overdose in the US included 1741 young adults in 2014 (National Institute on Drug Abuse, February, 2016a ). HRSBs can lead to sexually-transmitted diseases, unplanned pregnancy, and early parenthood (Van Ryzin et al. Reference Van Ryzin, Johnson, Leve and Kim2011). Socially, emerging adults who exhibit substance misuse and other health-risking behaviors may not transition into positive adult roles; they may show interpersonal difficulties, drop out of school, become parents while relatively young, or take on undesired full-time employment (Sussman, Reference Sussman2013). The costs of tobacco, alcohol, and illicit drug use to the US economy has been estimated at over $700 billion annually (National Institute on Drug Abuse, February, 2016b ); the costs of sexually transmitted infections (STIs) have been estimated at $16 billion in lifetime direct medical costs alone (National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, 2013).

The primary adolescent socializing environments (family and school/peer) exert substantial influence on risk and protective factors for substance misuse and other health-risking behaviors during adolescence. Protective factors include family relationship quality, monitoring, and parent-child warmth and affection; positive peer relationships distinguished by trust and affection; and school engagement, along with school task completion (Murray & Farrington, Reference Murray and Farrington2010; Stone et al. Reference Stone, Becker, Huber and Catalano2012). For this reason, preventive interventions designed to influence family-, school-, and peer-related risk and protective factors have been developed and tested with positive results (NRC-IOM, Reference O'Connell, Boat and Warner2009). The literature emphasizes the importance of providing preventive intervention during the developmental window when adolescents are just beginning to use substances and conduct problems are escalating (Offord & Bennett, Reference Offord, Bennett, Rutter and Taylor2002; Anthony, Reference Anthony2003; Chen et al. Reference Chen, Dormitzer, Gutierrez, Vittetoe, Gonzalez and Anthony2004; Spoth et al. Reference Spoth, Guyll and Shin2009a ).

There is an emerging literature on effects of universal preventive interventions implemented during young adolescence, especially effects on young adult substance misuse (Hawkins et al. Reference Hawkins, Kosterman, Catalano, Hill and Abbott2005; Poduska et al. Reference Poduska, Kellam, Wang, Brown, Ialongo and Toyinbo2008; Riggs et al. Reference Riggs, Chou and Pentz2009; Spoth et al. Reference Spoth, Trudeau, Shin, Ralston, Redmond, Greenberg and Feinberg2013b ; Botvin & Griffin, Reference Botvin and Griffin2014a ; Kellam et al. Reference Kellam, Wang, Mackenzie, Brown, Ompad, Or, Ialongo, Poduska and Windham2014). A subset of articles report on substance misuse outcomes among young adults for the same interventions that were implemented through the PROSPER delivery system (detailed in the Methods section, Spoth et al. Reference Spoth, Trudeau, Guyll, Shin and Redmond2009b , Reference Spoth, Trudeau, Redmond and Shin2014b , Reference Spoth, Trudeau, Redmond and Shin2016). The pattern of positive, long-term findings across multiple trials is noteworthy, especially considering that effects persist even after students leave the settings in which the interventions were implemented and setting-related factors are no longer operative (e.g. reduced negative peer influences, see Osgood et al. Reference Osgood, Feinberg, Gest, Moody, Ragan, Spoth, Greenberg and Redmond2013).

There is evidence that interventions addressing multiple risk and protective factors, designed to reduce substance misuse, also have crossover effects on other young adult health-risking behaviors or problems (e.g. conduct problem behaviors or internalizing outcomes)–even when no intervention content directly addresses those behaviors or problems (Trudeau et al. Reference Trudeau, Spoth, Randall, Mason and Shin2012; Kellam et al. Reference Kellam, Wang, Mackenzie, Brown, Ompad, Or, Ialongo, Poduska and Windham2014; Oesterle et al. Reference Oesterle, Hawkins, Kuklinski, Fagan, Fleming, Rhew, Brown, Abbott and Catalano2015). Specifically, a number of randomized controlled trials have demonstrated long-term crossover effects on emerging adult HRSBs (Botvin & Griffin, Reference Botvin and Griffin2014b ; Kellam et al. Reference Kellam, Wang, Mackenzie, Brown, Ompad, Or, Ialongo, Poduska and Windham2014; Spoth et al. Reference Spoth, Clair and Trudeau2014a ; Perrino et al. Reference Perrino, Pantin, Huang, Brincks, Brown and Prado2016).

The use of community-based delivery systems guided by key stakeholders in a community can create high quality implementation and sustainability of universal preventive interventions. In addition to the PROSPER model, Communities That Care (CTC) is a well-recognized community-based decision-making and program delivery model (Hawkins et al. Reference Hawkins and Catalano1992). In a multi-state prevention study of 24 small to moderate sized communities targeting youth ages 10–14, their families, and their schools, outcomes evaluated at age 19 showed a significant overall intervention effect across lifetime measures of substance use for males but not for females, nor for the full sample. ‘Lifetime abstinence’ from delinquency in the full sample was significantly higher in CTC communities; however, significant intervention effects were not found for specific delinquent or violent behaviors, or for recent substance misuse, substance use disorders or sexual risk behaviors (Oesterle et al. Reference Oesterle, Hawkins, Kuklinski, Fagan, Fleming, Rhew, Brown, Abbott and Catalano2015).

Here we examine long-term emerging adult outcomes of PROSPER, a delivery system that utilizes the outreach arm of the land grant university, the Cooperative Extension System (CES), to catalyze community teams to deliver school-based and family-focused interventions targeting middle school students. The PROSPER delivery system model (described in detail elsewhere; Spoth et al. Reference Spoth, Greenberg, Bierman and Redmond2004) consists of: (1) teams of community stakeholders linked with public schools and led by local CES staff, (2) Prevention Coordinators (PCs) connected with the land grant university's CES, and (3) a team of state-level university researchers and CES faculty. PCs serve as liaisons between the community and university teams, providing ongoing, proactive technical assistance to community teams to optimize team functioning and program delivery. (See online supplement for more detail about the PROSPER model).

Effectiveness of the PROSPER model (Spoth et al. Reference Spoth, Greenberg, Bierman and Redmond2004, Reference Spoth, Redmond, Shin, Greenberg, Clair and Feinberg2007c ) throughout middle and high school has been documented in earlier reports on this cluster randomized controlled trial, which began in 2001. Previously reported findings include effective participant recruitment (Spoth et al. Reference Spoth, Clair, Greenberg, Redmond and Shin2007a ), maintenance of high quality implementation (Spoth et al. Reference Spoth, Guyll, Lillehoj, Redmond and Greenberg2007b ), and sustainability of intervention delivery (Welsh et al. Reference Welsh, Chilenski, Johnson, Greenberg and Spoth2016). Earlier analyses of program impact on youth, parent, and family skills and behaviors–hypothesized to mediate impact on longer-term substance misuse–have shown significant effects on a range of outcomes. These include parenting and family outcomes (e.g. general child management, parent-child affective quality, parent-child activities, family environment), and youth outcomes (e.g. problem solving, assertiveness, association with antisocial peers, perceived substance use norms; see Redmond et al. Reference Redmond, Spoth, Shin, Schainker, Greenberg and Feinberg2009). Analyses have demonstrated significantly lower levels of substance misuse for the intervention group, relative to controls, for past month, past year, and growth trajectory slopes, especially for potentially more serious illicit substance misuse (e.g. marijuana, methamphetamine, prescription drug misuse), at both 4.5 and 6.5 years past baseline (grades 10 and 12, Spoth et al. Reference Spoth, Redmond, Clair, Shin, Greenberg and Feinberg2011, Reference Spoth, Redmond, Shin, Greenberg, Feinberg and Schainker2013a ). Further, these analyses showed that intervention effects for higher risk youth were comparable with or stronger than effects for lower risk youth. Finally, effects also were demonstrated on associated adolescent conduct problem behaviors through 6.5 years past baseline, with positive effects through 12th grade (Spoth et al. Reference Spoth, Trudeau, Redmond, Shin, Greenberg, Feinberg and Hyun2015).

Since youth have left high school our research focus has shifted to examining whether effects are sustained. Although a failure to sustain effects during the post-secondary follow up period would not negate beneficial effects at earlier ages (given the detrimental impact of adolescent substance misuse on relationships, disruptive behaviors, and academic functioning–as well as potential long-term brain and health effects of use during adolescent development), findings supporting sustained effects would provide further evidence of long-term benefits of universal prevention initiated during early adolescence. We also further explore whether intervention effects for higher-risk participants differ from lower-risk participants, as has been found in earlier reports.

Based on the literature cited above and the demonstrated PROSPER effects on proximal mediators and adolescent substance misuse, we hypothesized that effects on substance misuse would be sustained as study participants progress into emerging adulthood, during their first post-high school year, with additional intervention effects hypothesized for ancillary outcomes, including associated risk behaviors (antisocial behavior, HRSBs) and their consequences (STIs).

Methods

Community selection and assignment

A total of 28 rural communities were recruited from Iowa and Pennsylvania (14 in each state). Eligibility requirements included a community school district enrollment of 1300–5200 students and relevant stakeholder (extension and school district) agreement to random assignment, as well as a willingness and capacity to support PROSPER model implementation if assigned to the intervention condition. Following their enrollment, school districts were blocked on the basis of size and location, then randomized and informed of their assignment to the intervention condition. The participating universities’ Institutional Review Boards approved the study procedures. Additional details related to recruitment procedures are available in Spoth et al. (Reference Spoth, Clair, Greenberg, Redmond and Shin2007a ).

Sample and data collection

The study began with two successive cohorts of 6th graders enrolled in the 28 participating school districts. Figure 1 summarizes sample tracking over the waves of data collection. All enrolled 6th graders from the two cohorts were recruited for participation. Approximately 90% of the eligible sample provided baseline data. Most students were White (85%), 51% were female, 64% lived with both biological parents, and 31% received free or reduced-cost school lunchesFootnote ^† Footnote ¹ . The average age of participants was 11.8 years at baseline and 19.5 years for the current report.

Fig. 1. In-school survey and emerging adult follow up assessment: total participation by wave. *Note: Reported participation rates include all students in both study cohorts completing the in-school survey at the indicated wave through 12th grade. All students enrolled in the project school districts and in the targeted grades were eligible for participation, regardless of their participation in earlier survey waves, as a result, participation at later waves may exceed participation at pretest. Emerging adult assessments were conducted with randomly selected participants from the in-school assessment sample that completed 6th grade pretest assessments and were still enrolled in their baseline school district in the 9th grade.

In-class pretest self-report assessments were conducted with 6th graders during the fall semesters of 2002 (for Cohort 1) and 2003 (for Cohort 2). Follow-up assessments through high school were conducted annually in the springs of 6th–12th grade (i.e. from 0.5 to 6.5 years past baseline). On average, 88% of all eligible students completed in-school surveys across the eight data points, with slightly higher rates of participation at earlier data collection points.

Because of the high cost of following the entire sample into adulthood, after the spring of 12th grade, a randomly selected subsample of 1985 youth were recruited for continued follow-up. Participants who completed the 6th grade baseline assessment and were still enrolled in the same school district in the 9th grade were eligible for participation. Subsample selection was stratified by school district, gender, and risk status. Risk status was based on how many of the following five factors were reported by participants at baseline: lifetime gateway substance use (alcohol, cigarettes, or marijuana); conduct problem behaviors (at least 2 of 12); eligibility for the free/reduced cost school lunch program; lower family cohesion (dichotomized); and living with only one or no biological parents. Students were classified as higher-risk if they reported (a) any three or more of the five risk factors or (b) two risk factors, if gateway substance use and/or conduct problems were among the two. In order to have sufficient statistical power to investigate risk-related moderation effects when applying multilevel analytic models, higher-risk participants were oversampled. They comprised 37.4% of the participating subsample, v. 29.2% of the eligible sample. At age 19, participants could complete assessments either through a computer-assisted telephone interview or a web-based survey (16% and 84%, respectively). Sample and survey participation by school district and risk level is available online.

PROSPER partnership delivery system

In the communities assigned to the intervention condition, stakeholder teams of 8–12 individuals were formed, including the local CES-based team leader, a public school co-leader, representatives of local human service agencies (e.g. mental health, substance abuse), and parent and youth representatives. Teams selected a sequence of two interventions from a menu of evidence-based programs to be delivered, beginning with a family-focused intervention for 6th graders and their parents, followed by a school-based intervention implemented for the same cohort of youth in 7th grade. As part of the trial, communities administered these programs for two successive cohorts of students. (See the detailed description online.)

For their family-focused intervention, all 14 community teams selected the Strengthening Families Program: For Parents and Youth 10-14 (SFP 10–14). For their school-based intervention, four community teams selected Life Skills Training (LST), four selected Project Alert, and six selected the All Stars curriculum. Brief information on each program is in Table 1 (for more detail, see Spoth et al. Reference Spoth, Redmond, Shin, Greenberg, Clair and Feinberg2007c ).

Table 1. Brief description of PROSPER universal preventive interventions

Family intervention for 6th graders

Across the two successive cohorts of families of 6th graders, there were 142 SFP 10–14 program groups offered in the 14 intervention communities. A total of 1064 families attended at least one session, representing 17% of all eligible families. Of these, 90% attended at least four of the seven sessions and 63% attended at least six.

School interventions for 7th graders

The school-based program was implemented with Cohort 1 7th grade students in the second year of model implementation and with the Cohort 2 7th grade students the following year. Each school-based program was delivered in a class normally taken by all 7th grade students, generally by a trained classroom teacher (Spoth et al. Reference Spoth, Guyll, Lillehoj, Redmond and Greenberg2007b ).

Measures

Outcomes evaluated at age 19 were selected to (a) provide continuity with prior outcome reports, and (b) encompass developmentally-relevant young adult problem behaviors that have the potential for significant social-, health-, and economic-related harm. Measures were informed by those reported in previous studies (e.g. Spoth et al. Reference Spoth, Redmond and Shin2001) and included self-reported substance misuse, conduct problems in the form of antisocial behavior, HRSBs, and STIs. Substance misuse outcomes include lifetime use of illicit or non-prescribed drugs, drug- and alcohol-related problems, along with current use and frequency of use of more commonly used substances. Substance misuse questions were adapted from Monitoring the Future items (Johnston et al. Reference Johnston, O'Malley, Bachman, Schulenberg and Miech2015a ); items assessing antisocial behaviors were adapted from Elliott et al. (Reference Elliott, Huizinga and Ageton1985). Multi-item measures in the current report are count indices designed to assess cumulative numbers of risk behaviors or negative outcomes (in contrast to scales representing latent constructs assessed via multiple indicators); for this reason, alpha reliabilities were not calculated.

Lifetime substance misuse and related problems

Lifetime substance misuse measures included use of marijuana, cocaine, ecstasy, methamphetamine, LSD, non-prescribed narcotics, and amphetamines, scored as any use (1) vs. no use (0). The Illicit Substance Use Index includes lifetime use of five substances (dichotomized and summed); methamphetamine, ecstasy, LSD (or other hallucinogens, including mushrooms), cocaine, and GHB or Rohypnol. The Prescription Drug Misuse Index measured ‘overall’ prescription drug misuse and included three items (dichotomized and summed) addressing lifetime non-prescribed use of narcotics (e.g. Vicodin, Oxycontin, Percocet), amphetamines, and barbiturates.

Current use and frequency

More commonly used substances were measured with a, 1-month time frame; a 1-year time frame was applied for those substances less frequently used. These dichotomous measures indicated past-month drunkenness, past-month cigarette smoking, past-year marijuana use, and past-year use of narcotics not prescribed by a doctor. Past-year frequency of use was assessed for cigarette use, drinking, drunkenness, driving after drinking, marijuana use, and narcotic use. Frequencies were truncated at 150 times in the past year to prevent undue influence of outliers.

Drug- and alcohol-related problems

Indices were constructed to assess problems resulting from drug use and from alcohol use. Each index consisted of 15 dichotomous items adapted from the Short Inventory of Problems: Alcohol and Drugs (Blanchard et al. Reference Blanchard, Morgenstern, Morgan, Lobouvie and Bux2013) and addressed a range of substance-related problems and issues. Adaptation for the current study involved constructing measures to address drug- and alcohol-related problems separately, in contrast to the original measure, which assessed drug and alcohol problems jointly. Examples include: ‘You have failed to do what's expected of you because of your [drug/alcohol] use,’ and ‘You have had money problems because of your [drug/alcohol] use.’

HRSBs and STIs

HRSBs were assessed as an index of 11 dichotomously scored items. Examples include: lifetime intercourse, lifetime anal intercourse, number of intercourse partners (three or more), number of anal intercourse partners (more than one), past-year intercourse with someone they did not know well, and early onset of first intercourse (before age 14). STIs were assessed as an index of seven dichotomous items assessing lifetime diagnoses of gonorrhea, syphilis, herpes or warts, chlamydia, Hepatitis B, AIDS/HIV, and any other STI.

Antisocial behaviors

A count of antisocial and delinquent or illegal behaviors, adapted from Elliott et al. (Reference Elliott, Huizinga and Ageton1985), was constructed using 13 dichotomously-scored self-report items concerning past-year behaviors (behavior present v. absent). Example behaviors include: ‘Steal money or take something that did not belong to you,’ ‘Beat up or fight with someone because you were mad at them,’ ‘Drive a car recklessly,’ and ‘Sell stolen goods.’

Analyses

Multi-level ANCOVAs were conducted to test for intervention effects on outcomes. Binary outcomes were analyzed using SAS PROC GLIMMIX; other outcomes were analyzed using SAS PROC MIXED. These analytic procedures were selected to accommodate this study's cluster-randomized design and address relevant variance components across model levels. Analyzed models included the design factors of block (school district size and location), experimental condition, cohort, and state. An intent-to-treat approach was applied for all analyses. Effect size estimates are based on Cohen's d. In the last report on PROSPER high school outcomes, one-tailed significance levels and related p-values were applied because all intervention-control differences were in the expected direction at each earlier wave of data collection. For the current report, because less evidence was available to definitively support unidirectional hypotheses of effects at this developmental stage and for new measures of health-risking and other behaviors not previously tested with this sample, two-tailed p values are reported. Risk status was included as a post-hoc factor; Risk × Condition was included in order to assess risk moderation effects (conducted using the CONTRAST statement in SAS PROC MIXED and GLIMMIX). Risk-related moderation analyses were conducted to evaluate whether intervention effects for higher-risk youth were comparable to or stronger than effects for lower risk youth, as has been found in earlier analyses of PROSPER data. Although this risk measure is slightly different than the one used in earlier reports (Spoth et al. Reference Spoth, Redmond, Clair, Shin, Greenberg and Feinberg2011, Reference Spoth, Redmond, Shin, Greenberg, Feinberg and Schainker2013a ), it was selected because it is the measure that was used to stratify the young adult sample. Notably, 85% of those classified as higher- or lower-risk using this measure would be in the same risk classification category using the prior measure (which was based exclusively on gateway substance initiation at the baseline assessment).

Model-based relative reduction rates (RRRs) were calculated for binary outcomes to illustrate the practical significance of findings; they indicate the proportional reduction in behaviors in the intervention group relative to controls; that is, how much lower the estimated prevalence of a behavior is for those in the intervention group than in the control group, expressed as a percentage of the control group prevalence (e.g. if the estimated prevalences in the intervention and control groups were 40% and 50%, respectively, the RRR for the intervention group would be 20% [i.e.: (50–40%) ÷ 50% = 20%].

Results

Sample quality

Pretest equivalence of the two conditions was assessed; there were no significant differences on any sociodemographic measure (e.g. gender, age, race, school lunch status) or on any outcomes. Differential representation in the age 19 sample was assessed by examining whether the two-way interaction of Condition × Outcome pretest score predicted participation at age 19. No significant interactions were found.

Intervention effect estimates

Intervention main effect estimates (IMEE)

IMEEs are reported in Table 2. Results show significant IMEEs indicating lower levels of substance misuse in the intervention group across a range of substance use outcomes: Significant IMEEs were found for lifetime use of most individual illicit drugs (marijuana, cocaine, ecstasy, methamphetamine, LSD, non-prescription narcotics), as well as for the illicit and prescription drug misuse indices. In addition, significant IMEEs were found for the drug-related problems index and for the frequencies of cigarette and marijuana use. RRRs for significant binary outcomes favored the intervention group in all instances, and ranged from 9.4% (lifetime marijuana use) to 41.0% (lifetime methamphetamine use). There were no significant findings for current use measures, nor for HRSB or STI indices, or for the antisocial behavior index.

Table 2. Intervention-control differences for emerging adult outcomes

LS Means are model-based means. Analytic models include Block (school district size and location), State, Intervention Condition, and Cohort as design factors and Risk Status as a post-hoc factor. Analyses of binary outcomes were conducted using SAS PROC GLIMMIX; Relative Reduction Rates (RRRs) were calculated for binary outcomes. Analyses of continuous outcomes were conducted using PROC MIXED; Cohen's d was employed for effect size calculations.

To evaluate the sensitivity of results to the factors included the analytic model, we conducted analyses utilizing a simpler analytic model. Results were similar to those reported above.Footnote ² In addition, to further evaluate whether effects observed during high school were sustaining, diminishing or increasing, post hoc analyses also were conducted to examine substance new user rates after the post high school time point. Results showed those rates were lower for the intervention group for all outcomes, with one exception, but that they did not attain statistical significance (two-tailed).Footnote ³ These supplemental analyses are consistent with the suggestion of sustaining effects evidenced when applying the full analytic model based on the experimental design.

Risk moderation of intervention effect estimates

Risk moderation analyses found a significant Condition by Risk effect only for drug-related problems—the intervention effect estimate in this case was larger for the higher risk participants. However, that noted, the intervention-control difference was larger for the higher-risk participants than the lower-risk participants for most outcome variables (see online supplement for the table of risk moderation results). To illustrate the observed patterns of findings across study sites (school districts) by treatment condition and risk level, scatterplots for representative outcomes are provided in Fig. 2.

Fig. 2. Illustrative outcomes for each school district by intervention condition and risk level: Life time prevalence of (a) methamphetamine use; (b) marijuana use; (c) amphetamine use; and (d) norcotics use.