will allow for policy decisions made on the basis of the best scientific findings. These issues are discussed in more detail in Part III.


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.

Conclusion: Significant advances in statistical evaluation designs, measures, and analyses used in prevention research have contributed to improved understanding of the etiology of emotional and behavioral disorders and related problem behaviors since 1994.

Prevention methodology has enabled the use of refined statistical and analytical techniques to be used in an iterative manner to refine interventions, for example, by identifying components or groups for which the intervention is most successful and to further develop theories about causal mechanisms that contribute to the development of problems or to an intervention’s results.

Conclusion: Improved methodologies have also led to improved interventions, etiological theories, and theories of change.

The highest level of confidence in the results of intervention trials is provided by multiple well-conducted randomized trials. In addition, for some areas of prevention, the types of designs that are typically used have relatively limited ability to produce unambiguous causal inferences about intervention impact because of statistical confounding or inadequate controls, low statistical power, lack of appropriate outcome measures, or attrition. In these situations, it is important to develop additional evaluation designs that provide more rigorous testing of these interventions. Furthermore, few interventions have been tested for long-term outcomes despite the availability of appropriate methodologies. Several interventions have demonstrated effects on reducing multiple disorders and other related outcomes, such as academic performance. The value of preventive interventions would be significantly strengthened if long-term results could be demonstrated on a more consistent basis.

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