The intolerance of uncertainty scale: psychometric properties of the English version

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Abstract

Research is now suggesting that intolerance of uncertainty may be very important in understanding worry and may play a key role in the etiology and maintenance of worry. The present study attempted to further our understanding of intolerance of uncertainty by examining the psychometric properties of the English version of the Intolerance of Uncertainty Scale (IUS), which has already been validated in French. Factor analysis indicated that the IUS has a four-factor structure that represents the idea that uncertainty is stressful and upsetting, uncertainty leads to the inability to act, uncertain events are negative and should be avoided, and being uncertain is unfair. The IUS has excellent internal consistency, good test–retest reliability over a five-week period, and convergent and divergent validity when assessed with symptom measures of worry, depression, and anxiety. Overall, this study suggests that the IUS is a sound measure of intolerance of uncertainty and supports the idea that intolerance of uncertainty is an important construct involved in worry.

Introduction

Interest in the area of worry is rising and this has been reflected in the increase in research examining both worry and worry related phenomena (Freeston, Rhéaume, Letarte, Dugas, & Ladouceur, 1994; Mathews, 1993; Tallis & Eysenck, 1994). Worry can be defined as concern about future events in which there is uncertainty about the outcome and where the individual experiences feelings of anxiety (MacLeod, Williams, & Bekerian, 1991). Worry is common in both clinical and non-clinical populations and research has suggested that as high as 38% of individuals in the general population worry at least once a day (Tallis, Davey, & Capuzzo, 1994). Further, excessive and uncontrollable worry is the central feature of generalized anxiety disorder or GAD (DSM-IV; American Psychiatric Association, 1994). Given the level of worry in the general population and the role of excessive worry in the clinical disorder, GAD, it is important to identify key constructs related to worry in order to begin to establish how excessive worry develops and what factors are responsible for maintaining it.

Research into the area of worry has generally focused on worry themes and how much time is spent worrying (Davey, 1993; Dugas, Freeston, Doucet, Lachance, & Ladouceur, 1995). However, attention has shifted towards the examination of specific constructs related to worry (Freeston et al., 1994; Russell & Davey, 1993). For instance, researchers have begun to identify constructs that may be involved in the development and maintenance of worry (Dugas, Gagnon, Ladouceur, & Freeston, 1998; Wells & Carter, 1999). Research has linked the tendency to worry to positive and negative beliefs about the function of worry (Wells & Carter, 1999), the tendency to avoid upsetting mental imagery (Borkovec & Inz, 1990), negative problem orientation (Davey & Levy, 1999), and intolerance of uncertainty (Dugas et al., 1998).

Although a number of factors are associated with heightened levels of worry, one construct is beginning to emerge as a fundamental factor associated with excessive worry. Research is now suggesting that intolerance of uncertainty may be very important in understanding worry and may play a key role in the etiology and maintenance of worry (Freeston et al., 1994). Intolerance of uncertainty may be defined as the excessive tendency of an individual to consider it unacceptable that a negative event may occur, however small the probability of its occurrence (Dugas, Gosselin, & Ladouceur, 2001b). This suggests that someone who is intolerant of uncertainty will find many aspects of life intolerable given that it is filled with uncertainty and ambiguity.

Evidence for the connection between intolerance of uncertainty and worry comes from earlier studies that established that worriers possess a number of characteristics that set them apart from non-worriers. For example, worriers have been shown to require more information before arriving at a decision, which suggests that they have elevated evidence requirements (Tallis, Eysenck, & Mathews, 1991). The need for additional information may be a result of an intolerance for uncertainty and may be a means for lowering the level of uncertainty. Furthermore, worriers display more difficulties completing tasks that are ambiguous in nature compared to non-worriers (Metzger, Miller, Cohen, Sofka, & Borkovec, 1990). These findings suggest that worriers have a lower threshold for uncertainty, which impairs their performance on ambiguous tasks. In addition, worriers tend to define ambiguous situations or events as threatening (Butler & Mathews, 1983; Russell & Davey, 1993). This reaction suggests that worriers will have more difficulties when faced with uncertain situations given that they tend to interpret them in a negative way. Overall, the findings indicate that worriers have difficulty tolerating uncertainty, which provides the initial evidence for a specific construct related to worry: intolerance of uncertainty.

Recently, a number of studies have specifically linked intolerance of uncertainty to worry and have suggested that it may be one of the most significant factors involved in worry (Dugas, Freeston, & Ladouceur, 1997; Ladouceur, Talbot, & Dugas, 1997). Studies have demonstrated that intolerance of uncertainty and worry are highly related and that this relationship is not the result of shared variance with anxiety and depression (Dugas et al., 1997; Freeston et al., 1994). Given that anxious and depressive symptoms are significantly related to worry (Brown, Antony, & Barlow, 1992), these findings point to the important role intolerance of uncertainty may play in worry.

Furthermore, research has established intolerance of uncertainty as the most salient predictor of worry above positive beliefs about worry, negative problem orientation, and cognitive avoidance (Laugesen & Dugas, 2000; Robichaud & Dugas, 2000). These findings provide further support for the strong relationship between intolerance of uncertainty and worry, given that previous research has suggested that worry is highly related to beliefs about worry (Davey, Tallis, & Cappuzzo, 1996; Wells & Carter, 1999), problem orientation (Davey & Levy, 1999; Ladouceur, Blais, Freeston, & Dugas, 1998), and cognitive avoidance (Borkovec & Inz, 1990).

Recent studies have also begun to assess whether intolerance of uncertainty is specific to worry or whether it is a cognitive process involved in a number of emotional or anxiety related phenomena. Dugas and colleagues (2001a) assessed the relationship between intolerance of uncertainty, worry, obsessions/compulsions, and panic sensations. The results showed that, in a non-clinical sample, intolerance of uncertainty is highly related to worry, moderately related to obsessions/compulsions, and weakly related to panic sensations. In addition, research examining GAD, where the cardinal feature is excessive worry, has identified that level of intolerance of uncertainty distinguishes GAD patients from individuals suffering from other anxiety disorders (Ladouceur et al., 1999). This research supplies initial support for the idea that intolerance of uncertainty appears to have a stronger relationship with worry than other manifestations of anxiety.

Based on the strength of the relationship between intolerance of uncertainty and worry, researchers are now examining the possible causal role of intolerance of uncertainty in worry. Studies have shown that targeting intolerance of uncertainty in the treatment of excessive worry leads to changes in level of worry (Dugas & Ladouceur, 2000; Ladouceur et al., 2000a). Moreover, changes in intolerance of uncertainty generally precede changes in worry, over the course of treatment (Dugas & Ladouceur, 2000). A recent laboratory study has also demonstrated that manipulating an individual's level of intolerance of uncertainty resulted in changes in their level of worrisome thoughts, with increases in intolerance of uncertainty leading to more worry (Ladouceur, Gosselin, & Dugas, 2000b). According to Kraemer and associates (1997), establishing that changes in intolerance of uncertainty precede changes in worry and demonstrating that experimentally manipulating intolerance of uncertainty results in changes in worry, suggest that intolerance of uncertainty may be a causal risk factor for worry. Although more research is needed to confirm these initial findings, the results point to the role intolerance of uncertainty may play in the development and maintenance of worry.

Given the strong relationship between intolerance of uncertainty and worry and that changes in intolerance of uncertainty lead to changes in worry, it is important to consider whether they are distinct constructs. Worry has been commonly defined as concern about negative future events in which there is uncertainty surrounding the outcome and where the individual experiences feelings of anxiety (MacLeod et al., 1991). Although uncertainty is one aspect of worry, intolerance of uncertainty is the overall tendency of an individual to find it unacceptable that a negative event might occur, however small that probability. Worry might best be viewed as a mental act, where the individual thinks about the situation and possible outcomes. Whereas intolerance of uncertainty can be seen as a filter through which individuals view their environment, which might be best described as a predisposition to find uncertainty unacceptable. If an individual finds uncertainty unacceptable, when faced with uncertainty they may engage in excessive worrying. In this sense, worry may be seen as a product of intolerance of uncertainty.

One way to examine the distinction between worry and intolerance of uncertainty is to investigate their relationship with other factors. For example, Ladouceur and colleagues (1997) found that although intolerance of uncertainty and worry were highly related, they displayed different patterns of correlations with specific behavioral tasks. The researchers required participants to make decisions that varied on level of ambiguity and difficulty. The results indicated that worry was not correlated with performance on any of the behavioral tasks regardless of the amount of ambiguity or level of difficulty. Alternatively, intolerance of uncertainty was correlated with performance on moderately ambiguous tasks.

Another factor that may help differentiate between worry and intolerance of uncertainty can be found in the examination of possible gender differences on these constructs. Researchers have consistently identified gender differences on measures of worry with women reporting higher levels of worry. However, gender differences have not been found for intolerance of uncertainty (Freeston et al., 1994; Robichaud & Dugas, 2000). The differentiating patterns of correlations for worry and intolerance of uncertainty and the gender differences these constructs display, support the notion that although intolerance of uncertainty and worry are related, they are in fact different constructs.

Until recently, the research focusing on intolerance of uncertainty has been carried out exclusively in French-speaking populations, using a French measure of intolerance of uncertainty. In order to assess the relationship between intolerance of uncertainty and worry in English populations, an English version of the Intolerance of Uncertainty Scale (IUS) needs to be developed and validated. Furthermore, the concept of intolerance of uncertainty is still fairly new and additional research is needed to better delineate its relationship to worry. The present study will examine the psychometric properties of an English translation of the IUS in order to establish its reliability and validity, and further our understanding of intolerance of uncertainty.

The original French version of the IUS was developed to assess emotional, cognitive, and behavioral reactions to ambiguous situations, implications of being uncertain, and attempts to control the future (Freeston et al., 1994). Items on the IUS were devised from a pool of 74 statements that were generated to reflect different aspects of intolerance of uncertainty such as the consequences of being uncertain, how uncertainty reflects on a person, expectations about the predictability of the future, attempts to control the future, frustration around uncertainty, and ‘all-or-nothing responses’ to uncertainty. Items were assessed on face validity by four judges and items that were deemed irrelevant or redundant were discarded.

The remaining 44 items were administered to a group of 110 university students. The students were divided into three groups depending on whether they met GAD diagnostic criteria based on their responses to the Generalized Anxiety Disorder Questionnaire-Modified version (GADQ-M; Roemer, Borkovec, Posa, & Borkovec, 1995). The three groups included those meeting the criteria for GAD by questionnaire, those meeting only the somatic criteria for GAD by questionnaire, and finally those participants who met neither the full nor somatic criteria for GAD. Statistical analysis was used to identify the items that correctly distinguished between these three groups. Twenty-three items met this requirement and an additional four items were kept because of their high correlation with the Penn State Worry Questionnaire (PSWQ; Meyer, Miller, Metzger, & Borkovec, 1990), which is a general measure of the tendency to worry. The final 27 items on the IUS reflect the idea that uncertainty is unacceptable and leads to negative reactions.

The original study (Freeston et al., 1994) examined the psychometric properties of the French version of the IUS and examined the relationship between intolerance of uncertainty and measures of worry, anxiety, and depression. Factor analysis identified a five-factor solution that included: beliefs that uncertainty is unacceptable and should be avoided, being uncertain reflects badly on a person, uncertainty results in stress, frustration, and prevents action. The internal consistency of the scale was excellent (α=0.91) and its test–retest reliability over a five-week period was good (r=0.78; test–retest from Dugas et al., 1997). The scale was able to differentiate between groups of high and low worriers in a non-clinical sample, demonstrating criterion-related validity. Further, the IUS was highly correlated to measures of worry and to a lesser extent with measures of anxiety and depression, which supports the measure's convergent and divergent validity. In addition, once the shared variance of depressed and anxious symptoms was partialed out, the relationship to worry remained strong, suggesting that intolerance of uncertainty is specifically related to worry.

The IUS was translated from French to English using a well established method (Vallerand, 1989). Two independent translators translated the IUS into English. It was back translated by another independent translator, at which time problem items were identified and modified. Finally, a pilot version was administered to a small group of participants.

The present study, which assesses the English version of the IUS, followed a similar procedure to that used in the validation of the French version. The IUS was assessed for internal consistency, test–retest reliability, factor structure, and convergent and divergent validity using symptom measures of worry, depression, and anxiety. In addition, the IUS was assessed for its ability to distinguish between participants meeting all of the diagnostic criteria for GAD, based on their responses to a questionnaire, those meeting only some of the criteria for GAD, and participants meeting none of the criteria.

The study had a number of hypotheses. First, based on the findings from the original validation of the French version of the IUS, it was postulated that the measure would have excellent internal consistency and good test–retest reliability over a five-week period. Secondly, it was expected that factor analysis would reveal a similar factor structure when compared with the French version of the IUS. However, alternative factor analysis, which takes into account the intercorrelations between underlying factors on the IUS, was incorporated. This was expected to reveal an alternative factor structure that may better represent the underlying dimensions of the IUS. Moreover, it was proposed that intolerance of uncertainty would have a unique relationship with worry above and beyond demographics and mood. Finally, based on participants' responses to a questionnaire assessing GAD symptoms, it was hypothesized that the IUS would be able to discriminate between participants meeting all of the diagnostic criteria for GAD, those meeting only some of the criteria for GAD, and participants meeting none of the criteria.

Section snippets

Participants

Two hundred and seventy-six (N=276) participants were recruited through various undergraduate courses. There were 213 female participants and 62 males. Information regarding gender was missing for one participant. The mean age of participants was 22.6 (SD=5.05). Students were invited to participate at the start of a regular undergraduate course and participation was voluntary.

Instruments

The participants completed the following questionnaires in random order: the IUS, the PSWQ, the Worry and Anxiety

Results

Means and standard deviations for the measures are presented in Table 1. The means and standard deviations are consistent with those found for the validation of the French version of the IUS (Freeston et al., 1994). Moreover, the internal consistency of the IUS was excellent (α=0.94) and item-total correlations ranged from 0.36 to 0.77 and are displayed in Table 2. A group of 66 participants was re-tested on the IUS after five weeks, and the reliability coefficient was r=0.74.

Factor analysis

Discussion

Overall, the results confirm the study's predictions. The English version of the IUS has excellent internal consistency and good test–retest reliability. A four-factor structure was identified, which suggests that the items on the IUS represent the idea that uncertainty is stressful and upsetting, uncertainty leads to the inability to act, uncertain events are negative and should be avoided, and being uncertain is unfair. Although the French version of the IUS has a five-factor solution, the

Acknowledgements

This study was funded by the Fonds pour la Formation de Chercheurs et l'Aide à la Recherche du Québec.

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