Intolerance of Uncertainty (IUS)

1. Abstract

The Intolerance of Uncertainty Scale (IUS) is one of the most widely utilized and extensively validated psychometric instruments in clinical psychology and psychiatric epidemiology. Originally developed in French by Michel J. Dugas, Nicole Freeston, and Robert Ladouceur (1994) at Université Laval, and subsequently translated and validated in English by Kristin E. M. Buhr and Michel J. Dugas (2002), the scale operationalizes uncertainty as a dispositional cognitive vulnerability characterized by the tendency to react negatively on emotional, cognitive, and behavioral levels to uncertain situations and events. The original instrument comprises 27 self-report items (IUS-27) rated on a 5-point Likert-type scale ranging from 1 (not at all characteristic of me) to 5 (entirely characteristic of me). A psychometrically refined and widely adopted 12-item short form (IUS-12) was later established by R. Nicholas Carleton, Peter J. Norton, and Gordon J. G. Asmundson (2007), resolving historical debates regarding the underlying factor structure of the 27-item instrument.

Extensive psychometric investigations have demonstrated that the IUS possesses exceptional internal consistency, with Cronbach's alpha coefficients consistently exceeding .90 for the total score across diverse clinical and non-clinical populations, alongside robust test-retest reliability ($r = .74$ to $.78$ over multi-week intervals). While the original 27-item version demonstrated divergent factor solutions ranging from two to four dimensions across exploratory studies, the IUS-12 reliably isolates two robust, highly correlated second-order factors: Prospective Anxiety (fear of future uncertainty and proactive information seeking) and Inhibitory Anxiety (uncertainty-induced behavioral paralysis and cognitive freezing). The construct validity of the IUS is underpinned by marked convergent correlations with Generalized Anxiety Disorder (GAD), Obsessive-Compulsive Disorder (OCD), Major Depressive Disorder (MDD), and Social Anxiety Disorder (SAD), firmly establishing intolerance of uncertainty as a central transdiagnostic maintaining mechanism across the internalizing spectrum of psychopathology.

2. Keywords

Intolerance of Uncertainty, IUS-27, IUS-12, Prospective Anxiety, Inhibitory Anxiety, Generalized Anxiety Disorder, Transdiagnostic Vulnerability, Cognitive Behavioral Therapy, Psychometrics, Worry

3. Authors

The conceptual framework and initial French psychometric operationalization of the Intolerance of Uncertainty Scale (Échelle d'Intolérance à l'Incertitude; EII) were developed in 1994 by:

• Michel J. Dugas, Ph.D. — Professor of Psychology, Université du Québec en Outaouais and Concordia University, Montreal, Quebec, Canada. Dr. Dugas is an internationally recognized authority on the cognitive-behavioral etiology and treatment of generalized anxiety disorder and excessive worry.
• Mark H. Freeston, Ph.D. — Professor of Clinical Psychology, Newcastle University, Newcastle upon Tyne, United Kingdom. Dr. Freeston has published pioneering work on cognitive intrusions, obsessive beliefs, and the mechanics of uncertainty.
• Robert Ladouceur, Ph.D. — Emeritus Professor of Psychology, School of Psychology, Université Laval, Quebec City, Quebec, Canada. Dr. Ladouceur is a pioneer in experimental cognitive psychopathology, behavioral medicine, and the empirical modeling of anxiety disorders.

The standard English adaptation and initial psychometric validation (IUS-27) were published by:

• Kristin E. M. Buhr, Ph.D. — Registered Psychologist, Director of the North Shore Stress and Anxiety Clinic, North Vancouver, British Columbia, Canada; formerly affiliated with Concordia University, Montreal.
• Michel J. Dugas, Ph.D. — Concordia University, Montreal, Quebec, Canada.

The psychometrically optimized 12-item short form (IUS-12) and its definitive two-factor structural validation were developed by:

• R. Nicholas Carleton, Ph.D., R.D. Psych. — Professor of Clinical Psychology, Department of Psychology, University of Regina, Regina, Saskatchewan, Canada.
• Peter J. Norton, Ph.D. — Professor of Psychology, School of Psychological Sciences, Monash University, Melbourne, Australia; formerly University of Houston, Texas, USA.
• Gordon J. G. Asmundson, Ph.D., FRSC — Professor of Psychology, Department of Psychology, University of Regina, Regina, Saskatchewan, Canada; Editor-in-Chief of the Journal of Anxiety Disorders.

4. Purpose

The primary purpose of the Intolerance of Uncertainty Scale is to provide a standardized, psychometrically rigorous self-report measure of an individual's dispositional inability to tolerate the subjective discomfort provoked by the absence of salient, conclusive, or sufficient information. Originally formulated within an etiology-specific framework to explain the pathogenesis of chronic, uncontrollable worry in Generalized Anxiety Disorder (GAD), the scale measures beliefs regarding the unacceptability of uncertainty, the tendency to perceive unexpected occurrences as inherently negative, and the inclination to experience life's ambiguities as cognitively and behaviorally disabling.

In clinical settings, the IUS serves several critical diagnostic and therapeutic functions. Clinicians utilize the scale during baseline psychodiagnostic evaluations to measure cognitive vulnerability thresholds, guide functional behavioral analyses, and distinguish normative apprehension from clinical disorders characterized by pathological cognitive avoidance. In Cognitive Behavioral Therapy (CBT)—most notably within Dugas and Ladouceur's Cognitive Model of GAD—the scale tracks therapeutic progress and treatment outcomes. Therapeutic modules target cognitive appraisals of uncertainty through behavioral experiments, exposure to uncertainty, and problem-solving training. Reductions in IUS scores mediate symptom reduction in excessive worry, health anxiety, panic disorder, and obsessive-compulsive checking rituals.

In empirical psychopathology, the IUS is used extensively to evaluate transdiagnostic vulnerabilities. While early research treated intolerance of uncertainty as pathognomonic of GAD, contemporary clinical science recognizes the construct as a fundamental transdiagnostic vulnerability factor operating across major depressive episodes, social anxiety, eating disorders, post-traumatic stress disorder (PTSD), and autism spectrum conditions. Researchers use the IUS to examine structural relationships between neural reactivity to threat ambiguity (e.g., heightened amygdala activation and altered insular cortex functioning) and individual differences in subjective distress during laboratory uncertainty paradigms.

5. Psychological Construct

Intolerance of uncertainty (IU) is defined as a dispositional characteristic resulting from a broad set of catastrophic beliefs about uncertainty and its implications. In their foundational theoretical works, Dugas, Buhr, and colleagues conceptualized IU as an overarching cognitive filter through which an individual assesses ambiguous information, novel scenarios, and probabilistic outcomes. Within this framework, high-IU individuals view uncertainty as stressful, upsetting, unfair, incapacitating, and indicative of impending disaster.

Dimensions of the Construct

Through empirical factor analyses of the IUS-27 and its short form (IUS-12), the construct has been delineated into distinct, intercorrelated psychological dimensions:

• Prospective Anxiety (Desire for Predictability and Cognitive Preoccupation): This dimension encompasses anticipatory cognitive and affective distress regarding future ambiguous events. Individuals scoring high in prospective anxiety exhibit an intense drive to foresee all potential outcomes, eliminate ambiguity, and secure absolute certainty prior to decision-making. Representative behaviors include compulsive reassurance-seeking, repetitive hyper-vigilance, excessive contingency planning, and list-making. The core cognition asserts that unforeseen events are inherently disruptive and that one must continuously look ahead to avoid negative surprises (e.g., Item 10: “One should always look ahead so as to avoid surprises”; Item 18: “I always want to know what the future has in store for me”).
• Inhibitory Anxiety (Behavioral and Cognitive Paralysis): In contrast to prospective striving, inhibitory anxiety captures the direct paralyzing impact of uncertainty on active functioning. Individuals characterized by high inhibitory anxiety experience executive disruption, behavioral avoidance, and decision-making inertia when faced with an uncertain environment. Uncertainty acts as a total cognitive roadblock: individuals report feeling frozen, unable to proceed with tasks, disengaged from problem-solving, and helpless (e.g., Item 12: “When it's time to act, uncertainty paralyses me”; Item 14: “When I am uncertain, I can't go forward”).
• Beliefs that Uncertainty is Unfair and Reflects Negatively on the Self: As measured primarily in the full 27-item instrument, this facet captures maladaptive self-referential schemas and moralized evaluations of ambiguity. Individuals evaluate personal uncertainty as a sign of incompetence, disorganization, or cognitive weakness (e.g., Item 2: “Being uncertain means that a person is disorganized”; Item 13: “Being uncertain means that I am not first rate”). Simultaneously, they exhibit externalized resentment regarding the absence of universal guarantees in human existence (e.g., Item 4: “It's unfair not having any guarantees in life”).

6. Theoretical Framework

The development of the IUS is grounded in cognitive-experimental psychopathology and contemporary learning theory. The theoretical foundations rest on the Dugas and Ladouceur Cognitive Model of Generalized Anxiety Disorder, alongside subsequent formulations such as the Dual-Factor Model of IU proposed by Carleton et al. (2007) and the evolutionary framework of Uncertainty as Threat formulated by Carleton (2016).

The Cognitive Model of Worry (Dugas, Gagnon, Ladouceur, & Freeston, 1998)

Within this architecture, intolerance of uncertainty functions as the foundational catalyst in a sequential cognitive cascade that culminates in clinical anxiety. The model hypothesizes four interrelated components:

1. Intolerance of Uncertainty: The central vulnerability factor. It lowers the cognitive threshold required to perceive a situation as ambiguous. When confronted with ambiguous stimuli, individuals with high IU interpret ambiguous cues as threatening and dangerous.
2. Positive Beliefs About Worry: Beliefs that worrying helps anticipate danger, prevent negative outcomes, motivate constructive action, or demonstrate emotional care.
3. Negative Problem Orientation: A pervasive lack of confidence in one's problem-solving capabilities, accompanied by the perception of everyday problems as personal threats rather than normal challenges.
4. Cognitive Avoidance: The utilization of verbal-linguistic worry to suppress distressing somatic arousal and catastrophic mental imagery.

In this framework, IU serves as the underlying soil from which pathological worry emerges. Because uncertainty is interpreted as intolerable, the individual engages in repetitive mental simulations (worry) in an effort to artificially generate certainty, mentally audit every permutation of future catastrophe, and avoid the aversive experience of surprise.

Uncertainty / Ambiguous Cue $\rightarrow$
Heightened Threat Perception (High IU) $\rightarrow$
Prospective Worry & Information Seeking $\rightarrow$
Inhibitory Paralysis & Avoidance

Carleton's “Fear of the Unknown” Paradigm

R. Nicholas Carleton (2016) elevated the construct from an anxiety-disorder-specific vulnerability to a foundational, transdiagnostic evolutionary mechanism: the fear of the unknown. Carleton posited that human cognition is evolutionarily wired to prioritize survival by anticipating potential threats. Organisms that fail to recognize the danger of the unknown face severe fitness costs. When an organism possesses an elevated baseline sensitivity to missing information, any scenario lacking total predictability is registered neurobiologically as equivalent to imminent physical peril. This theoretical orientation explains why IU is systematically observed across diverse clinical presentations, including social anxiety (where the unknown is others' evaluations), OCD (where uncertainty relates to contamination, harm, or moral responsibility), panic disorder (uncertainty regarding interoceptive bodily cues), and depression (uncertainty regarding future agency and efficacy).

7. Validity

The psychometric validity of the Intolerance of Uncertainty Scale has been rigorously corroborated across clinical, community, and university cohorts in dozens of cross-cultural contexts.

Construct and Convergent Validity

Construct validity is evidenced by strong, statistically significant correlations with theoretical correlates of cognitive distress and emotional dysregulation. In their initial English validation of the IUS-27, Buhr and Dugas (2002) documented substantial convergent correlations between the IUS and:

• The Penn State Worry Questionnaire (PSWQ): $r = .60$ to $.67$, demonstrating a robust link between IU and excessive, uncontrollable worry.
• The State-Trait Anxiety Inventory – Trait Form (STAI-T): $r = .55$ to $.65$, illustrating the relationship between IU and generalized emotional vulnerability.
• The Beck Depression Inventory (BDI / BDI-II): $r = .52$ to $.63$, capturing the shared variance between cognitive paralysis and depressive helplessness.

Carleton et al. (2007, 2012) replicated these correlations using the IUS-12, confirming that Prospective Anxiety correlates more robustly with proactive cognitive rumination and worry ($r = .55$ to $.68$ with the PSWQ), whereas Inhibitory Anxiety correlates more strongly with behavioral inertia, depression, and social avoidance ($r = .58$ to $.64$ with the BDI-II; $r = .52$ with the Social Interaction Anxiety Scale).

Discriminant Validity

Discriminant validity has been demonstrated through hierarchical regression analyses and structural equation modeling. Buhr and Dugas (2006) showed that after controlling for trait anxiety, general neuroticism, and baseline depression, intolerance of uncertainty consistently accounts for a significant portion of unique incremental variance in pathological worry ($R^2\Delta$ ranging from $.06$ to $.12$, $p < .001$). Furthermore, IU maintains distinct boundary separations from related constructs such as perfectionism, fear of negative evaluation, and locus of control, showing that it does not represent an artifact of generalized negative affectivity.

Predictive and Criterion Validity

The predictive utility of the scale is robust in longitudinal, experimental, and treatment-outcome designs. In laboratory threat paradigms, individuals scoring in the upper quartile of the IUS demonstrate elevated skin conductance responses, prolonged reaction times in dot-probe tasks presenting ambiguous cues, and pronounced self-reported distress when exposed to tasks with variable reinforcement schedules. Clinically, pre-treatment to post-treatment reductions in IUS total scores strongly predict remission rates in GAD and OCD following standardized CBT protocols, with change scores in IU mediating long-term symptom relief (Dugas et al., 2010).

8. Reliability

The IUS exhibits strong, consistent reliability across language adaptations, clinical populations, and age groups.

Internal Consistency

For the full 27-item scale (IUS-27):

• In the original French validation by Freeston et al. (1994), internal consistency was excellent, with a Cronbach's alpha of $\alpha = .91$.
• In the English validation conducted by Buhr and Dugas (2002), the total scale demonstrated an internal consistency coefficient of $\alpha = .94$. Corrected item-total correlations ranged from $.36$ to $.77$, with a median item-total correlation of $.61$.

For the abbreviated 12-item scale (IUS-12):

• Carleton, Norton, and Asmundson (2007) reported a Cronbach's alpha of $\alpha = .91$ for the total score, with subscale coefficients of $\alpha = .85$ for Prospective Anxiety (Items 1–7) and $\alpha = .85$ for Inhibitory Anxiety (Items 8–12).
• Cross-cultural replications (e.g., Helsen et al., 2013 in Dutch; Khawaja & Yu, 2010 in Australian samples) have confirmed alpha values between $.87$ and $.93$ for the total score and $.82$ to $.89$ across subscales.

Test-Retest Stability

Temporal stability assessments demonstrate that the IUS measures a stable, trait-like disposition:

• Buhr and Dugas (2002) administered the IUS-27 across a 5-week test-retest interval in a non-clinical cohort, yielding an intraclass test-retest reliability coefficient of $r = .74$ ($p < .001$), indicating substantial longitudinal stability.
• In a 2-week stability assessment of the IUS-12, Carleton et al. (2007) documented a test-retest coefficient of $r = .78$, with no statistically significant mean shifts in Prospective or Inhibitory Anxiety subscale scores across the assessment window.

9. Factor Analysis

The dimensional structure of the Intolerance of Uncertainty Scale has been the focus of considerable methodological refinement within clinical psychometrics.

Exploratory Factor Analyses of the IUS-27

Initial investigations of the 27-item instrument yielded varying factor solutions:

• Freeston et al. (1994) initially reported a single overarching general factor accounting for the majority of the variance in French samples.
• Buhr and Dugas (2002) conducted exploratory factor analysis (EFA) using principal axis factoring with oblimin rotation on the English IUS-27, identifying a four-factor structure explaining 49.3% of the variance: (1) Uncertainty is stressful and upsetting; (2) Uncertainty leads to the inability to act; (3) Uncertain events are negative and should be avoided; and (4) Being uncertain is unfair. However, several items exhibited complex cross-loadings ($> .30$ on multiple factors), and factor intercorrelations were high ($r = .48$ to $.69$), indicating that a four-factor solution might over-partition the variance.
• Other researchers (e.g., Norton, 2005) identified alternative two-factor or three-factor solutions across diverse ethnic cohorts, highlighting sample dependency and item redundancy in the full 27-item scale.

Confirmatory Factor Analysis and Development of the IUS-12

To resolve these structural ambiguities, Carleton, Norton, and Asmundson (2007) conducted rigorous confirmatory factor analyses (CFA) across independent university and community cohorts ($N = 811$ and $N = 463$). Testing competing models (unidimensional, four-factor, and various two-factor solutions), they isolated 12 psychometrically robust items that systematically aligned into an oblique two-factor structural model:

The two-factor IUS-12 model demonstrated exceptional goodness-of-fit indices across subsequent confirmatory structural equation modeling studies (e.g., Carleton et al., 2007; Helsen et al., 2013; Carleton et al., 2012):

• Comparative Fit Index (CFI) $ge .96$
• Tucker-Lewis Index (TLI) $ge .95$
• Root Mean Square Error of Approximation (RMSEA) $le .053$ (90% CI [.042, .064])
• Standardized Root Mean Square Residual (SRMR) $le .041$

Bifactor modeling and hierarchical CFA further confirm that while Prospective and Inhibitory subscales capture distinct facets, they load significantly onto a general, higher-order Intolerance of Uncertainty latent dimension, supporting both subscale-level profiling and total-scale score interpretations.

10. Instrument / Measurement Tool

The Intolerance of Uncertainty Scale is structured as an objective, self-administered rating instrument.

• Instrument Designation: Intolerance of Uncertainty Scale (Full Version: IUS-27; Short Form: IUS-12).
• Administration Modality: Paper-and-pencil questionnaire, computerized digital survey, or clinician-facilitated rating.
• Item Count:
  • Full Version: 27 items.
  • Abbreviated Version: 12 items.
• Response Scale: 5-point Likert-type scale with designated verbal anchors:
  • 1 = Not at all characteristic of me
  • 2 = Slightly characteristic of me
  • 3 = Somewhat characteristic of me
  • 4 = Very characteristic of me
  • 5 = Entirely characteristic of me
• Scoring Procedures:
  • IUS-27 Scoring: All 27 items are positively keyed (no reverse-scored items). A continuous total score is derived by summing all responses, yielding a theoretical range of 27 to 135. Higher scores indicate greater intolerance of uncertainty. Subscale scores can be derived based on the four-factor Buhr & Dugas (2002) model, though total score interpretation is standard.
  • IUS-12 Scoring: All 12 items are positively keyed. Summing all items yields a total score ranging from 12 to 60.
    • Prospective Anxiety Subscale: Sum of items 1, 2, 3, 4, 5, 6, and 7 (Score range: 7 to 35).
    • Inhibitory Anxiety Subscale: Sum of items 8, 9, 10, 11, and 12 (Score range: 5 to 25).
• Target Population: Adolescents and adults (ages 16–80+). Normative benchmarks exist for university students, community adults, and clinical cohorts with anxiety and mood disorders.
• Completion Time: 5 to 10 minutes for the IUS-27; 2 to 3 minutes for the IUS-12.

11. Permissions & Fee and Test Year

• Year of Initial Publication: 1994 (original French instrument; Freeston et al.); 2002 (validated English IUS-27; Buhr & Dugas); 2007 (validated English IUS-12; Carleton et al.).
• Copyright Status: The original psychometric instruments are copyrighted by their respective originating authors and the psychological journals in which they appeared (Association for Advancement of Behavior Therapy / Elsevier / American Psychological Association).
• Usage Licensing & Fees: The IUS-27 and IUS-12 are designated as open-access for non-commercial academic research, empirical inquiry, and individual clinical assessment purposes. No licensing fee or royalty payment is required for non-commercial use. Researchers and clinicians must cite the foundational validation articles (Buhr & Dugas, 2002; Carleton et al., 2007) when disseminating findings. Commercial applications, including proprietary digital health integration, automated SaaS platforms, or commercial clinical trials, require formal copyright clearance and written permission from the copyright holders.

12. References

Buhr, K. E. M. (2001). Examination of the relationship between intolerance of uncertainty and worry (Master's thesis). Concordia University, Montreal, Quebec, Canada. https://www.collectionscanada.gc.ca/obj/s4/f2/dsk3/ftp04/MQ64017.pdf

Buhr, K., & Dugas, M. J. (2002). The Intolerance of Uncertainty Scale: Psychometric properties of the English version. Behaviour Research and Therapy, 40(8), 931–945. https://doi.org/10.1016/S0005-7967(01)00092-4

Buhr, K., & Dugas, M. J. (2006). Investigating the construct validity of intolerance of uncertainty and its unique relationship with worry. Journal of Anxiety Disorders, 20(2), 222–236. https://doi.org/10.1016/j.janxdis.2004.12.004

Carleton, R. N. (2016). Fear of the unknown: One fear to rule them all? Journal of Anxiety Disorders, 41, 5–21. https://doi.org/10.1016/j.janxdis.2016.03.011

Carleton, R. N., Collimore, K. C., & Asmundson, G. J. G. (2010). “It's not just the judgements—It's that I don't know”: Intolerance of uncertainty as a predictor of social anxiety. Journal of Anxiety Disorders, 24(2), 189–195. https://doi.org/10.1016/j.janxdis.2009.10.007

Carleton, R. N., Gosselin, P., & Asmundson, G. J. G. (2010). The Intolerance of Uncertainty Index: Replication with an English sample. Psychological Assessment, 22(2), 396–406. https://doi.org/10.1037/a0019230

Carleton, R. N., Mulvogue, M. K., Thibodeau, M. A., McCabe, R. E., Antony, M. M., & Asmundson, G. J. G. (2012). Increasingly certain about uncertainty: Intolerance of uncertainty across anxiety and depression. Journal of Anxiety Disorders, 26(3), 468–479. https://doi.org/10.1016/j.janxdis.2012.01.011

Carleton, R. N., Norton, M. A. P. J., & Asmundson, G. J. G. (2007). Fearing the unknown: A short version of the Intolerance of Uncertainty Scale. Journal of Anxiety Disorders, 21(1), 105–117. https://doi.org/10.1016/j.janxdis.2006.03.014

Dugas, M. J., Gagnon, F., Ladouceur, R., & Freeston, M. H. (1998). Generalized cognitive-behavioral model of generalized anxiety disorder. In Cognitive therapy of anxiety disorders: Science and practice (pp. 41–64). Guilford Press.

Freeston, M. H., Rhéaume, J., Letarte, H., Dugas, M. J., & Ladouceur, R. (1994). Why do people worry? Personality and Individual Differences, 17(6), 791–802. https://doi.org/10.1016/0191-8869(94)90048-5

Helsen, K., Van den Bussche, E., Vlaeyen, J. W. S., & Goubert, L. (2013). Confirmatory factor analysis of the Dutch Intolerance of Uncertainty Scale: Comparison of the full and short version. Journal of Behavior Therapy and Experimental Psychiatry, 44(1), 21–29. https://doi.org/10.1016/j.jbtep.2012.07.004

13. Items of the Scale (Questionnaire)