Preventing Mental, Emotional, and Behavioral Disorders Among Young People Progress and Possibilities (2009) / Chapter Skim
Currently Skimming:
10 Advances in Prevention Methodology
10 Advances in Prevention Methodology
Pages 263-294
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to respond to specific scientific and practical questions being raised in ongoing evaluations of prevention programs. In particular, evaluations of preventive interventions that have been conducted as randomized field trials (Brown and Liao, 1999; Brown, Wang, et al., 2008)
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It brings together prevention scientists conducting cutting-edge randomized trials and expert methodologists who are committed to addressing the key design and analytic problems in prevention research. PSMG has attempted to anticipate needs for methodological development and to have new methods ready when the trials demand them (Albert and Brown, 1990; Brown, Costigan, and Kendziora, 2008)
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. We discuss first the uses of randomized preventive trials, which have led to an extraordinary increase in knowledge about prevention programs (see Chapters 4 and 6)
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Evaluating a Preventive Intervention with a Randomized Preventive Trial Randomized preventive trials are central in evaluating efficacy (impact under ideal conditions) or effectiveness (impact under conditions that are likely to occur in a real-world implementation)
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A theory of change is then used to identify an existing intervention or to develop a new preventive intervention aimed at these target risk or protective factors. In a program aimed at preventing substance abuse and delinquency among children who are returning to parental care from a foster placement, a parent training intervention might be designed to reduce punitive statements, to enhance communication with the child, and to improve linkages with the child's own parents and teacher in preparation for the critical transition period of return to the family of origin.
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Evaluating the Effects of Preventive Interventions Some randomized preventive trials examine questions of program efficacy, or impact under ideal conditions, and can also help determine whether the intervention affects hypothesized mediators and proximal targets in expected ways. These efficacy trials are conducted in settings in which the intervention fidelity is maintained at a high level, usually by having trained researchers deliver the intervention rather than by individuals from the community.
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; such wait-list designs, however, allow for only short-term, not long-term evaluations of impact. Using Preventive Trials to Improve an Intervention An equally important goal of randomized preventive trials is to search for ways to improve in an intervention.
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In another example, a study of young adolescents at risk for delinquency tested three active preventive intervention conditions against a control: a parent intervention alone, a peer-based intervention, and a combined peer and parent intervention. The parent condition alone produced a beneficial outcome; the combined peer–parent intervention produced results similar to the control; and the peer-based intervention produced more delinquency than did the other conditions (Dishion, Spracklen, et al., 1996; Dishion, Burraston, and Poulin, 2001; Dishion, McCord, and Poulin, 1999)
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Because one-quarter of the parents made enrollment decisions contrary to the assigned condition, the intent-to-treat analysis, which makes no allowance for deviations from the assigned condition, provides a biased estimate of the causal effect of the intervention. Use of Preventive Interventions to Test and Elaborate Theories of Change and Development Although using preventive interventions to test and elaborate theories of change and development is the least practical reason for conducting trials, it may be the most important for generating new knowledge.
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, for example, identified psychological well-being and lower positive expectancy toward drug use as key mediators between competence skills and later substance use. Preventive trials can also examine the causal role of a particular risk factor when it is targeted by an intervention.
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How beneficial is a preventive intervention program compared with another type of intervention? Preventive interventions can be compared not only with one another, but also with a service-based or treatment approach.
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As it expands, the number of teachers requiring train ing and supervision increases, and therefore a scalability trial tests the system-level responses to these demands. Using Randomized Preventive Trials to Meet the Needs of the Community Field experiments of prevention programs are guided by federal requirements to maintain protection of human subjects.
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. Scientific Logic Behind the Use of Randomized Preventive Trials Some in the scientific community believe that it is not possible to conduct field trials of prevention programs to produce sound causal inferences about these programs.
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. Because many preventive interventions are carried out in these existing social fields, they are tested in preventive trials that often randomize whole groups rather than randomize at the level of individuals in the groups (Raudenbush, 1997; Murray, 1998; Brown and Liao, 1999)
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. Other approaches can also be followed to increase statistical power in group-based randomized trials.
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. BUILDING RIGOROUS CAUSAL INFERENCES FROM RANDOMIZED FIELD TRIALS At the time of the 1994 IOM report, prevention scientists generally had a limited understanding of the underlying framework for drawing causal conclusions about their interventions from randomized and nonrandomized experiments.
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or corrections are made for missing data at baseline. Possible Inferences in Response to Self-Selection One innovative change in the way prevention trials are now analyzed is to account for self-selection factors that differentiate those who choose to participate in the prevention program from those who do not.
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Distinct Ethical Issues for Conducting Preventive Trials In treatment studies, the existing standards for ethical conduct of research dictate that it is improper to withhold an effective, safe treatment from participants. Thus because there are successful treatments for schizophrenia, it would be inappropriate and unethical to evaluate a new antipsychotic drug in a randomized trial that assigned some psychotic individuals to receive a placebo.
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This approach was used for practical reasons in a large preventive trial aimed at preventing the spread of HIV among Thai military conscripts through changes in sexual practices. Rather than randomly assign individuals in the same company to two different conditions, companies were matched within battalions and then randomly assigned to an active behavioral intervention or a passive diffusion model (Celentano, Bond, et al., 2000)
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. As one begins to look at how a complex preventive intervention affects individuals with specific genetic characteristics, it would not be surprising to find allelomorphic variation in outcomes, or that positive as well as negative outcomes can occur for those with a single allele.
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Evaluating the Components of Interventions and Adaptive Interventions Trials to examine the functioning of distinct components of an intervention may be needed, as when a comprehensive prevention program, such as Life Skills Training (see Box 6-1) , has multiple components or modules that have been incorporated over the years.
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Program components can be tested by themselves by randomizing which teachers, or other such intervention agents, are to receive no training, low training, or high training. Using the Internet for Randomized Preventive Trials The Internet presents new opportunities to deliver preventive interventions to a diverse and expanding audience and to test the interventions in large randomized trials.
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, which would include a phone or face-to-face interview for a stratified sample of study participants. Sequencing of Preventive Trials and Selective Long-Term Follow-Up In most health research, trials are staged in a progression from basic to clinical investigations to broad application in target populations, allowing for an ordered and predictable expansion of knowledge in specific areas (e.g., Greenwald and Cullen, 1985)
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In other situations, there may be no opportunity to conduct a true randomized trial to assess the effects of a defined intervention, because the community is averse to the use of a randomization scheme, because ethical considerations preclude conducting such a trial, or because funds and time are too limited. Even so, many opportunities remain to conduct careful evaluations of prevention programs, and much can be gained from such data if they are carefully collected.
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. This type of design can provide valuable information, particularly when it supports a hypothesized developmental model involving known mediators that lead to expected prevention targets.
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Using Growth Models Most theories of change in prevention research posit an evolving effect on the individual that varies over time as new developmental stages are reached. Although it should be possible to detect intervention effects at a critical transition period using an outcome measured at a single time point, it is also possible to examine the impact of interventions using longitudinal data to show differences in individuals' developmental trajectories or growth patterns (e.g., repeated measures of aggression or symptoms)
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Intervention effects can be modeled for each pattern of growth in risk behaviors over time, such as stable low levels of drug use, escalating levels, stable high levels, and decreasing levels. The results of such analyses may show, for example, that although a universal intervention reduces drug usage among those who begin using drugs early, it may have the unintended effect of increasing drug usage in what began as a low-risk group.
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When the previous IOM report was written, most published analyses of intervention impact simply deleted any missing cases. Now most impact analyses make use of full maximum likelihood methods (Dempster, Laird, and Rubin, 1977)
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Finally, the ability to model the costs as well as the effectiveness of different preventive interventions for communities
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CONCLUSIONS AND RECOMMENDATIONS Since the 1994 IOM report, new methodological tools have been developed that enable more nuanced analysis of outcomes, more sophisticated designs that enable randomized assignment, and more reliable outcomes. These advances in modern statistical approaches have been particularly useful in the context of field trials of preventive interventions that face particular randomization challenges not usually relevant to clinical trials.
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. Given that most preventive interventions are designed to mitigate developmental processes that can lead to mental, emotional, and behavioral disorders and problems over time, assessment of whether proximal outcomes at one developmental period are sustained in distal outcomes at a later developmental period is needed.
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. Priority areas should also include approaches that link neuroscience methods and clinical research with epidemiology and prevention in understanding the etiology of mental health and of disorders and approaches that link theories developed through neuroscience research with preventive intervention approaches designed to test causal mechanisms (see Chapter 5)
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