Most importantly, participants in the dissonance intervention showed a significantly lower risk for onset of clinically significant eating pathology relative to assessment-only controls (6% versus 15%), which amounts to a 60% reduction in the number of expected cases that would have theoretically emerged in this high risk sample in the absence of the intervention. These results suggest that for every 100 young women who complete this intervention, approximately 9 fewer should show onset of eating pathology. It was also noteworthy that healthy weight participants showed a statistically significant 61% reduction in risk for future onset of eating pathology relative to assessment-only controls, which suggests that for every 100 young women who complete the program, approximately 9 fewer should show onset of this eating disturbance. An examination of the rates of onset for the three different eating disorders revealed that the effects were primarily driven by differential risk for onset of bulimic pathology, which was 3% for dissonance participants, 5% for healthy weight participants, 6% for expressive-writing controls, and 12% for assessment-only controls (suggesting that the dissonance intervention produced a 75% reduction in risk for bulimic pathology onset relative to assessment-only controls). Although it will be vital to replicate these effects in an independent trial, these findings are very encouraging because to our knowledge, no other eating disorder prevention program has been shown to reduce risk for future onset of clinically significant eating pathology. In addition, these appear to be the first eating disorder prevention programs to produce effects that persist through 3-year follow-up, though we acknowledge that most prevention programs that have produced effects for eating pathology have not been evaluated in trials with a long-term follow-up; thus it is possible that other programs may produce long-term effects.
Of equal importance was the evidence that participants in the healthy weight intervention showed a 55% reduction in risk for obesity onset and less increases in BMI relative to assessment-only controls over the 3-year follow-up because a recent meta-analytic review suggested that no obesity prevention program has produced effects that persist this long (Stice, Shaw, & Marti, 2006
). Again, however, because most obesity prevention trials have not included long-term follow-ups, some of the weight-gain prevention effects that have been observed from pretest to posttest in other trials may persist over longer-term follow-up. The fact that the two prevention programs evaluated in this trial have produced significant intervention effects for both eating disorder symptoms and weight gain (Stice, Shaw, Burton, et al., 2006
) is noteworthy because very few programs have produced effects for both of these important public health problems (Stice, Shaw et al., 2007
). Prevention programs that produce effects for more than one physical or psychiatric problem have greater public health utility and cost effectiveness than those that produce effects for only one problem.
Interestingly, although the effects that reflect reductions in initial symptoms and risk factors were greatest at earlier follow-ups, the prophylactic effects were stronger at the latter follow-ups (e.g., reduced risk for eating pathology onset). This pattern of findings probably emerged because the incidence of eating pathology and obesity were greatest at the latter follow-ups. These results imply that it is important to conduct longer-term follow-up in prevention trials to fully characterize the effects of prevention programs. The fact that the average follow-up in eating disorder prevention trials is only 4 months (Stice, Shaw et al., 2007
) suggests this is an important limitation to address.
Another encouraging aspect of the findings is that results provided further evidence that each intervention significantly outperformed an active alternative intervention. The dissonance program produced significantly stronger effects on thin-ideal internalization, body dissatisfaction, and psychosocial impairment than the expressive writing intervention; the healthy weight program produced significantly stronger effects on thin-ideal internalization and increases in BMI than expressive writing controls. There was even evidence that the healthy weight intervention was significantly more effective than the dissonance intervention at slowing the rate of weight gain, and that the dissonance intervention was significantly more effective than the healthy weight intervention in reducing functional impairment.
It was also striking that this high-risk sample of young women with self-identified body image concerns showed such high rates of onset of eating pathology (15%) and obesity (17%) in the assessment-only condition over the 3-year follow-up. The fact that new cases of eating pathology continued to emerge at 3-year follow-up (at which point participants had a mean age of 20) implies that the peak period of risk for onset of eating pathology extends into young adulthood for this high-risk population, in contrast to findings from studies of normative samples (e.g., Lewinsohn et al., 2000
). This also implies that it would be important to extend the follow-up periods of future eating disorder prevention trials to capture this peak period of risk. In addition, these results underscore the importance of delivering prevention program to this high-risk population.
However, there were also discouraging aspects of the results. First, many of the effects that were observed at posttest did not persist through follow-up. For instance, for the continuous outcomes 73% of the effects were significant at posttest, but only 47% were significant at 3-year follow-up. Although this might not be surprising given that these interventions were only three hours in duration (plus the time to complete the homework), this pattern of findings suggests that a priority for future trials will be to investigate methods of bolstering the persistence of intervention effects. Second, the effects that were observed were somewhat more likely to emerge when the interventions were compared to the assessment-only control condition rather than the expressive-writing placebo control condition. However, even the current treatments of choice for certain disorders, such as cognitive-behavior therapies for bulimia nervosa, binge eating disorder, and depression, typically do not significantly outperform alternative interventions over long-term follow-ups, although they often do in the short-term (Brent et al., 1997
; Fairburn et al., 1995
; Wilfley et al., 2002
). Because these same preventive and treatment interventions produce greater reductions than observed in assessment-only control groups, this pattern of findings may suggest that if an individual engages in any
type of intervention, they may be more willing to try alternative methods of resolving the problem behavior (though there was no evidence of differential ancillary treatment across conditions in our trial) or that expectances contribute more to long-term effects than short-term effects. Third, although important prophylactic effects emerged, they were limited in number. This pattern of findings, and the more general evidence that prevention programs rarely produce prophylactic effects (Horowitz & Garber, 2006
; Stice, Shaw et al., 2006
; Stice, Shaw et al., 2007
), suggests that another important priority for future prevention trials will be to determine how to better reduce risk for future onset and escalation in eating disorder symptoms.
The findings from this report and the previous report on the short-term effects of these interventions (Stice, Shaw, Burton et al., 2006
) suggest that these two programs have somewhat different strengths. Relative to healthy weight participants, dissonance participants showed significantly greater reductions in thin-ideal internalization, body dissatisfaction, dieting, negative affect, and eating disorder symptoms at posttest, in negative affect at 6-month and 1-year follow-up, and in psychosocial impairment by 3-year follow-up. This is noteworthy because very few eating disorder prevention programs have been shown to outperform structurally equivalent alternative prevention programs, though other trials have provided evidence that the dissonance intervention outperformed alternative prevention programs (Becker et al., 2006
; Green et al., 2005
). In contrast, relative to dissonance participants, healthy weight participants showed significantly greater reduction in risk for obesity onset by 1-year follow-up and significantly less weight gain through 3-year follow-up. There were no other instances wherein either intervention produced significantly stronger effects than the other intervention. Overall, this pattern of findings suggests that the dissonance intervention produces stronger effects for eating pathology and risk factors, whereas the healthy weight intervention produces stronger weight gain prevention effects.
It is noteworthy that both interventions produced effects for eating pathology and weight gain that persisted over long-term follow-up because the two programs have such different content. One potential explanation is that they both make use of strategic self-presentation (Cialdini & Goldstein, 2004
) to promote a reduction in maladaptive attitudes and behaviors; in the dissonance program participants engage in activities in which they voluntarily and publicly criticize the thin-ideal to reduce thin-ideal internalization and in the healthy weight program participants publicly commit to making healthy improvements to their dietary intake and physical activity to promote lasting healthy lifestyle changes. Theoretically, people who make public commitments to change behavior are more likely to enact these changes because of the increased accountability and a desire to be consistent in their actions. Interestingly, the one other prevention program that produced effects for eating pathology that persisted through long-term follow-up (Neumark-Sztainer et al., 1995
) also used role-play exercises involving strategic self-presentation (refusing pressure to be thin). In addition, both interventions make use of motivational enhancement techniques (Miller, 1983
); in the dissonance program participants discuss the costs of pursuing the thin-ideal and in the healthy weight intervention participants discuss the costs of obesity and the benefits of maintaining a healthy weight. Theoretically, these exercises increase the likelihood that participants will engage in the program and make changes to their maladaptive attitudes and behaviors, emphasizes individual responsibility, and promotes internal attribution for attitudinal and behavioral change. In line with this interpretation, dismantling studies indicate that the dissonance-induction procedures used in the dissonance program contribute to the observed effects of this intervention (Green et al., 2005
; Roehrig et al., 2006
). In addition, our meta-analytic review of eating disorder prevention programs (Stice, Shaw et al., 2007
) suggested that other prevention programs that have not produced intervention effects for eating pathology that persist through follow-up typically have not included strategic self-presentation and motivational enhancement exercises. Future research should consider ways of increasing the use of strategic self-presentation and motivational enhancement components to these and other prevention programs, in an effort to produce larger and more persistent intervention effects.
Within this context, it should be noted that the healthy weight intervention also uses the foot-in-the-door technique (Cialdini & Goldstein, 2004
), wherein a small request for behavior change that is easy to make is followed by a request for a related larger and more difficult behavior change. Theoretically, people are more inclined to acquiesce to the larger request when it is made after completion of the smaller request because they feel motivated to maintain behavioral consistency. Specifically, we ask participants to make minor behavioral changes regarding diet and activity level in the first session, but then follow these requests in subsequent sessions by requests to make additional and more substantial health behavior changes. It might be fruitful to explore using this persuasion principle in eating disorder prevention programs to enhance the effects.
Because this trial required contrasts between four conditions, involved multiple follow-up points, and included a broad array of outcomes, it was necessary to perform numerous inferential tests to investigate all of the hypotheses and fully characterize the intervention effects. Thus, there is a possibility that some of the findings reported here are false positive findings (Type I errors). Although it is important to consider this issue, two considerations suggest that the findings are valid. First, the number of significant effects reported here (40%) is eight times higher than the 5% that would be expected based on chance. Second, the fact that these two interventions have produced effects for many of these outcomes across three studies that we have conducted (e.g., Stice et al., 2000
; Stice et al., 2003
) and at least 10 trials that have been conducted by 7 independent research groups (e.g., Becker et al., 2006
; Green et al., 2005
; Matusek et al., 2004
; Mitchell et al., 2007
; Roehrig et al., 2006
) leads us to believe that these effects are not simply false positive findings. Nonetheless, results should be interpreted with some caution.
Although we improved upon many prior prevention trials by using random assignment, an active control condition, blinded diagnostic interviews, a large and ethnically diverse sample, and ecologically valid outcomes, the current study had several limitations. First, we relied on self-report data, with the exception of the direct measures of height and weight, which introduces the possibility of reporter bias. It might be useful for future prevention trials to collect multiple-informant data and objective biological data. Second, we used a simple approach to assess intervention fidelity; future trials that compare multiple interventions should employ skilled clinicians as raters and should assess the finer details of these interventions. Third, these blended selective-targeted prevention programs were delivered to a relatively small portion of high-risk adolescent girls from the larger population from which we sampled (e.g., typically about 7% of female students in a given school). Future trials should explore the approach of targeting multiple high-risk populations (e.g., those with elevated body dissatisfaction, dieting, or negative affect), as this may increase the reach of selective prevention programs. Within this context, it is important to note that prior trials have suggested that the dissonance intervention produces effects for unselected populations (e.g., Becker et al., 2006
; Green et al., 2005
Implications for Prevention and Future Research
The present findings imply it will be vital to determine ways to enhance the magnitude and duration of the effects of these two prevention programs. Future trials should test whether increasing the number and duration of intervention sessions, using in-person, mail-based, or internet-based booster sessions, adjunctive interventions (e.g., an internet based support group), or an intervention component targeting parents improves effects. We also recommend evaluating whether an increased use of persuasion principles from social and clinical psychology represent a method of enhancing effects of the interventions, including strategic self-presentation, motivational enhancement exercises, and the foot-in-the-door approach. The findings from Green and associates (2005)
suggest that making the in-session and home exercise more effortful, increasing accountability (e.g., by videotaping sessions), and increasing the perception that participation is voluntary may increase the effects for the dissonance program, as these are processes that increase dissonance induction. In addition, future research should investigate whether the dissonance and healthy weight interventions can be integrated to produce even stronger effects. Researchers should also consider adapting components from other eating disorder prevention programs that produced promising intervention effects (e.g., Neumark-Sztainer et al., 1995
More generally, it will be important for future prevention trials to use longer-term follow-ups to better understand the persistence of intervention effects, as most trials have not included long-term follow-ups. Furthermore, additional efforts should be devoted to designing interventions that affect multiple physical and mental health problems because this would improve the public health impact of prevention efforts. One promising approach might be to target general risk factors that predict onset of several pathological conditions, rather than risk factors that are specific to only one condition. It might also be useful to test whether prevention programs that effectively reduce a pathological behavior (e.g., binge eating) also reduce other public health problems arising from that behavior (e.g., obesity and depression). Furthermore, it will be vital to conduct effectiveness trials to determine whether these interventions will produce effects in the real world (e.g., among all high schools in a district) when delivered by endogenous providers (e.g., school counselors). To date, virtually all prevention programs have been evaluated in efficacy trials that test whether the interventions are effective when delivered under optimal conditions by highly trained and supervised experts. Finally, researchers should initiate dissemination studies to determine how best to train large numbers of providers, whether these providers can deliver the interventions with fidelity and competence, and to identify barriers to the successful implementation of these interventions on a large-scale basis. We believe that additional programmatic and rigorous research will bring us closer to realizing the goal of reducing the overall prevalence of eating disorders through prevention.