Many people find uncertainty distressing, but for some, it may become overwhelming and drive persistent anxiety, worry, and avoidance. This tendency is called intolerance of uncertainty (IU), and appears across many mental health conditions, including generalised anxiety, social anxiety, depression, and obsessive-compulsive disorder, which is why researchers describe it as a transdiagnostic feature.
A type of therapy called Cognitive Behavioural Therapy for Intolerance of Uncertainty (CBT-IU) has been shown to reduce anxiety in previous trials. What remains to be known is how uncertainty changes when targeted directly, and whether the same mechanism applies across diagnoses. IU has mostly been measured using questionnaires, which indicate whether people find uncertainty difficult, but not what is actually happening when they encounter it. Recent research suggests that IU is not a single trait but a set of differences in how people estimate different kinds of uncertainty. Therefore, in addition to standard questionnaires, computer-based tasks will be used to explore an "uncertainty fingerprint" for each participant, capturing different aspects of uncertainty processing in a way that self-report measures cannot.
In this study, the investigators are comparing CBT-IU, adapted to work across disorders, against Applied Relaxation. Applied relaxation is a well-established therapy that teaches people to notice and release physical tension but does not focus on uncertainty. Adults with high IU and anxiety symptoms (regardless of formal diagnosis) will be randomly allocated to one of the two 12-session group therapies. The investigators will measure anxiety and IU using standard questionnaires as the primary outcomes. Additionally, cognitive tasks will be used to measure the uncertainty fingerprint before therapy, immediately after, and three months later. The aim is to test whether reductions in IU are specific to CBT-IU rather than shared with an equally credible therapy that does not target uncertainty. Going beyond self-reports, the trial will then begin to resolve which specific aspects of uncertainty processing change, so that future treatments can be more precisely targeted and better matched to each person.
Normal or corrected-to-normal vision
Fluency in English
Capable of giving informed consent
Live locally/ within commutable distance to Cambridge
High risk of suicidal intent or self-harm (defined as an affirmative response on item 9 of the PHQ-9 above the clinical threshold, and/or corresponding clinical risk indicators during the SCID-5 interview)
Engagement with any other psychological treatment within the 3 months prior to the study or during the study period
Current diagnosis of obsessive-compulsive disorder (OCD)
Current substance use disorder
Parallel
Group Transdiagnostic Cognitive Behavioural Therapy for Intolerance of Uncertainty (CBT-IU)
BehavioralManualised group-based transdiagnostic CBT-IU delivered over 12 sessions by a clinical psychologist and a co-facilitator. The modular intervention integrates evidence-based frameworks, including the Dugas and Robichaud CBT-IU model for GAD (Dugas \& Robichaud, 2007) and the Making Friends with Uncertainty (Mofrad et al., 2020). Modules cover: 1. Psychoeducation and awareness of uncertainty responses (Session 1-2); 2. Recognising and monitoring uncertainty (Sessions 3-4); 3. Structured problem-solving skills (Sessions 5-6); 4. Behavioural experiments with individualised uncertainty hierarchies (Session 7-10); and 5. Relapse prevention and maintenance planning (Sessions 11-12). Between-session home practice is set each week. Treatment fidelity is monitored via a per-session checklist, weekly clinical supervision with the trial lead, and independent rating of random audio-recorded sessions against the manual.
Group Transdiagnostic Applied Relaxation (AR)
BehavioralManualised group-based transdiagnostic Applied Relaxation delivered over 12 sessions by a clinical psychologist and a co-facilitator, following Öst (1987). Content is organised into five modules: 1. Psychoeducation, self-monitoring and 16-muscle-group Progressive Muscle Relaxation (PMR; Sessions 1-2); 2. Stepwise condensing of PMR (16-muscle → 7-muscle → 4-muscle → release-only → cue-controlled → rapid relaxation); introduction of diaphragmatic breathing; early cue detection. 3. Afterwards, the application phase begins, in which participants use rapid relaxation proactively at the first signs of tension (Sessions 3-7). Safe-place imagery and self-soothing as additional relaxation pathways (Sessions 8-9). 4. Participants consolidate all learned techniques into a personal Applied Relaxation toolkit (Session 10); and 5. Relapse prevention and maintenance planning. Between-session home practice is set each week. Treatment fidelity is monitored identically to the CBT-IU arm.
Intolerance of Uncertainty Scale (IUS-12)
The reduced Intolerance of Uncertainty Scale (IUS-12; Carleton et al., 2007; Freeston et al., 1994) is a 12-item self-report measure of cognitive, emotional, and behavioural reactions to uncertainty. Higher scores indicate greater intolerance of uncertainty.
Generalized Anxiety Disorder-7 (GAD-7)
The GAD-7 (Spitzer et al., 2006) is a 7-item self-report measure of generalised anxiety symptom severity. Scores range from 0 to 21; higher scores indicate greater severity.
Patient Health Questionnaire (PHQ-9)
The PHQ-9 (Kroenke et al., 2001) is a 9-item self-report measure of depressive symptom severity. Scores range from 0 to 27; higher scores indicate greater severity.
Work and Social Adjustment Scale (WSAS)
The WSAS (Mundt et al., 2002) is a 5-item self-report measure of functional impairment attributed to mental health problems across work, home management, social leisure, private leisure, and close relationships. Items are rated from 0 to 8. Higher scores indicate greater impairment.
Penn State Worry Questionnaire (PSWQ)
The PSWQ (Meyer et al., 1990) is a 16-item self-report measure of pathological worry validated in GAD populations. Higher scores indicate more pervasive and uncontrollable worry.
Affective Response to Daily Uncertainty Scale (ARDUS)
The ARDUS (Wang et al., 2026) is a 37-item self-report measure of how often individuals experience negative affect (worry, anxiety, low mood, or concern) when faced with uncertainty across six everyday domains: academic/professional, climate, financial, health, political, and social. Items are rated on a 6-point Likert scale from 0 (Never) to 5 (Always), with an additional option indicating that the type of uncertainty has not been encountered in the past year. Higher scores reflect greater affective reactivity to daily uncertainty.
Working Alliance Inventory - Short Revised (WAI-SR)
The WAI-SR (Hatcher \& Gillaspy, 2006) is a 12-item measure of perceived agreement with therapy goals and tasks and therapeutic bond, used to compare therapeutic alliance across arms.
Beliefs About Psychological Services scale (BAPS)
The BAPS (Ægisdóttir \& Gerstein, 2009) is an 18-item self-report measure of attitudes and beliefs about seeking professional psychological help. Items are rated from 1 to 6, and yield three subscale scores covering intent to seek services, stigma tolerance, and expertness. Higher scores indicate more positive beliefs about psychological services.
Credibility/Expectancy Questionnaire (CEQ)
The CEQ (Devilly \& Borkovec, 2000) is a 6-item self-report measure of how credible a participant finds a treatment rationale and how much improvement they expect from it. The measure assesses credibility and expectancy. Items are rated on mixed scales, most from 1 to 9 and two of the expectancy items from 0% to 100%, with higher scores indicating greater perceived credibility and stronger expectation of improvement.
Group Climate Questionnaire (GCQ)
The GCQ (MacKenzie, 1983) is a 12-item measure of participants' perception of the group's therapeutic environment, used as a process/quality measure of the group intervention.
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Medical Research Council Cognition and Brain Sciences Unit
Lead sponsor
University of Cambridge
Collaborator
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