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Growing evidence suggests that intolerance of uncertainty (IU) is a cognitive vulnerability that is a central feature across diverse anxiety disorders, including generalized anxiety disorder (GAD). Although cognitive behavioral therapy (CBT) has been shown to reduce IU, it remains to be established whether or not reductions in IU mediate reductions in worry. This study examined the process of change in IU and worry in a sample of 28 individuals with GAD who completed CBT. Changes in IU and worry, assessed bi-weekly during treatment, were analyzed using multilevel mediation models. Results revealed that change in IU mediated change in worry (ab = −0.20; 95% CI [−.35, −.09]), but change in worry did not mediate change in IU (ab = −0.16; 95% CI [−.06, .12]). Findings indicated that reductions in IU accounted for 59% of the reductions in worry observed over the course of treatment, suggesting that changes in IU are not simply concomitants of changes in worry. Findings support the idea that IU is a critical construct underlying GAD.

Intolerance of uncertainty (IU), the dispositional tendency to experience fear of the unknown, is considered to be an important factor in the development and maintenance of anxiety disorders (Carleton, 2012). IU includes beliefs that uncertainty is threatening, stressful, and anxiety provoking, as well as the desire to avoid situations where uncertainty and ambiguity may be present (Buhr and Dugas, 2002 and Dugas et al., 2001). Although IU likely contributes to multiple anxiety disorders (e.g., Carleton, 2012), the most comprehensive conceptual model of the relationships between IU and anxiety psychopathology was designed primarily to account for symptoms of generalized anxiety disorder (GAD; Dugas, Gagnon, Ladouceur, & Freeston, 1998). GAD features worry, defined as “repetitive, uncontrollable thoughts about negative life events” (Segerstrom, Tsao, Alden, & Craske, 2000), as a predominant symptom (American Psychiatric Association, 2013). For those high in IU, the possibility of negative outcomes is proposed to trigger maladaptive behavioral and cognitive reactivity (e.g., biased interpretations of the situation, increased need for information during decision-making) that serve to increase worry and anxiety (Dugas et al., 2005, Dugas and Robichaud, 2007 and Ladouceur et al., 2000). Moreover, IU contributes to other problematic cognitive processes, including poor problem orientation and cognitive avoidance, which conjointly and paradoxically maintain worry and anxiety (Dugas & Robichaud, 2007). Data from several treatment outcome studies indicate that anxiety interventions impact IU, and suggest that IU may play a role in maintaining anxiety. Dugas and colleagues (e.g., Dugas et al., 2003, Dugas et al., 2010 and Dugas and Ladouceur, 2000) have developed a cognitive-behavioral intervention specifically to address IU as part of a comprehensive treatment for GAD, which has been shown to effectively decrease IU and other symptoms (e.g., worry, depression). Other types of CBT interventions that do not feature an explicit focus on IU also appear to reduce IU in GAD (e.g., Boswell et al., 2013, Hewitt et al., 2009 and van der Heiden et al., 2012). Thus, preliminary evidence suggests that IU is malleable with CBT interventions in individuals with GAD. Establishing IU as a process relevant to symptom reduction is critical to validate cognitive theories and to identify treatment strategies to optimize therapeutic outcomes (Kazdin, 2007 and Smits et al., 2012). The aforementioned treatment outcome studies provide evidence that IU changes from pre to post treatment, but the process by which IU changes relative to other symptoms has not been empirically established. For example, it is possible that reducing IU lessens worry, or that IU levels are lower at the end of treatment because worry or general anxiety symptoms have decreased. One case-controlled study suggests that reductions in IU precede reductions in worry in treatment for GAD (Dugas & Ladouceur, 2000). An analogue study of exposure-based treatment components also suggested that reductions in IU predicted subsequent reductions in worry (Goldman, Dugas, Sexton, & Gervais, 2007). Further support for a causal relationship between IU and worry comes from experimental psychopathology studies indicating that manipulating IU appears to impact worry (Ladouceur et al., 2000 and Meeten et al., 2012). However, models suggesting reduction in IU as a mediator of reductions in worry longitudinally over the course of treatment have yet to be confirmed empirically. Evaluating whether or not changes in IU precede and account for symptom change during treatment provides a more rigorous test of the hypothesis that IU is a core construct that perpetuates worry and anxiety (Kazdin, 2007). The present study examined the process of change in IU and worry in a sample of individuals with GAD who completed a CBT program. The goal of the analyses was to test the proposed mediational relationship outlined in models of GAD and worry—specifically that reductions in IU would account for reductions in worry over the course of treatment. Using data from an open trial of a transdiagnostic CBT treatment protocol for anxiety, changes in IU and worry assessed at pre-treatment and bi-weekly during treatment were analyzed using multilevel mediation procedures. We hypothesized that reductions in IU would mediate subsequent reductions in worry across sessions.

Cognitive models suggest a causal relationship between IU and worry, and reduction of IU has been proposed as a potential process by which psychological treatments may reduce worry. We sought to examine the relationship between reduction in worry and IU over the course of CBT for individuals with GAD. Consistent with our hypothesis, results revealed that IU and worry ameliorated over time, and that reductions in IU significantly mediated subsequent reductions in worry over the course of treatment. The reverse mediation model indicated that the converse patterns of mediation did not hold; change in IU was not significantly mediated by change in worry over time. Theoretical models and empirical data suggest that IU is a cognitive vulnerability to anxiety (Carleton, 2012). IU plays a central role in the model of GAD outlined by Dugas and colleagues (e.g., Dugas & Robichaud, 2007), which proposes that individuals with high levels of IU exhibit negative psychological reactions to uncertain situations, and tend to respond to uncertain situations with worry. Findings indicating mediation of reduction in worry by reduction in IU add to a growing body of literature suggesting that IU is not only associated with worry but may be causally linked to it (e.g., Ladouceur et al., 2000 and Meeten et al., 2012). Consistent with trials of CBT for anxiety (e.g., Boswell et al., 2013, Dugas et al., 2003, Dugas et al., 2010, Ladouceur et al., 2000 and Mahoney and McEvoy, 2012), our data suggests that CBT-based interventions effectively reduce IU for individuals with GAD. While reductions in IU have been shown to precede reductions in worry in short-term exposure exercises with high worriers (Goldman et al., 2007), our analysis of treatment data extends examination of change over time to a sample of clinically anxious individuals completing CBT. Data not only suggest a reduction in IU with treatment, but longitudinal observation of changes across constructs establishes temporal precedence of change in a group of individuals completing treatment. Reducing IU during treatment might promote subsequent reductions in worry in a number of ways. First, cognitive behavioral treatments aimed at decreasing anxiety promote behavioral exposure to uncertain situations, which would likely decrease reactivity to uncertainty. If anxiety surrounding uncertain situations decreases (corresponding to an increased tolerance for uncertainty), a concomitant decrease in avoidance behaviors (i.e., worry) could be reasonably expected to follow. Treatment components might also alter beliefs about uncertainty. For example, following treatment individuals may be less likely to believe that worry is an effective or necessary way to plan for uncertain outcomes, or may no longer believe that uncertainty is inherently bad. However empirical evidence is needed to evaluate the potential of these explanations to account for the mediation findings observed in the present study. Given that IU accounts for reductions in worry over time, incorporating an emphasis on IU may be helpful within treatment protocols for disorders characterized by worry. In the present treatment protocol, IU was not an explicit intervention target. Individuals were encouraged to complete exposure exercises wherein they confronted situations that invoked anxiety generally. However, exposure to uncertainty was undoubtedly present during anxiety exposures and associated cognitive restructuring may have touched upon negative beliefs about uncertainty more broadly. Indeed, prior studies found that CBT programs do reduce IU (e.g., Mahoney & McEvoy, 2012), and in some cases IU may change more during interventions that are not IU specific as compared to those that directly aim to target IU (van der Heiden et al., 2012). Nonetheless, deliberately including situations with high levels of uncertainty within an exposure hierarchy framework while addressing negative beliefs about the uncertain potential for negative outcomes (e.g., treatment as described by Dugas et al., 2010) may be even more successful in producing IU reductions. To date, no studies have compared the process of change between intervention approaches with respect to reductions in IU. In addition, it remains to be established if individual-level characteristics, such as an individual's level of IU or other factors, would make him/her a more ideal candidate for a specific type of approach. Future research is needed to address ways to maximize treatment effectiveness while also personalizing treatments (Kazdin, 2007 and Smits et al., 2012). Several study limitations should be noted. First, selection of participants based on neuroimaging inclusion and exclusion criteria limits generalizability (e.g., participants utilizing certain medications or substances were excluded). The effect size observed for reductions in the PSWQ-A was also modest. It is possible that aspects of the transdiagnostic CALM program (as opposed to GAD-specific CBT programs) did not optimally target worry-related symptoms. Alternatively, the particular sample treated may have possessed features that negatively influenced treatment response as compared to prior studies, or the abbreviated PSWQ may have been less sensitive to change than the full version. Future studies would ideally include a broader range of participants with a larger sample and incorporate different treatment types to address whether or not such patterns of change are consistent for other individuals in other intervention modalities. In addition, recent evidence supports the role of both IU and worry across diverse anxiety disorders (e.g., OCD, panic disorder; Boswell et al., 2013 and Carleton, 2012), and suggests that reductions in IU have the potential to mediate change in worry and other anxiety-related constructs across different conditions. Further research is warranted to examine how IU changes over time in different disorders, and how IU reductions may influence change in worry or other disorder-specific constructs (e.g., obsessions or compulsions in OCD). The design did not allow for comparison of mediation processes to a control group. Thus, one cannot conclude that the changes in worry and IU were directly attributable to the treatment components per se, as opposed to non-specific factors or the passage of time. Finally, assessments were conducted every other session only within the acute phase of treatment. Patterns of change within the measured sessions or beyond the acute phase of treatment thus cannot be determined. In summary, reductions in IU mediated subsequent reductions in worry over the course of CBT in a sample of individuals diagnosed with GAD. Results are consistent with theoretical models outlining the importance of IU as a cognitive vulnerability to GAD that operates via its effect on worry. Thus, IU is malleable with treatment and targeting IU during treatment may be one effective strategy to reduce worry.