Extended Abstract
1. Introduction
Intolerance of uncertainty significantly contributes to the experience of anxiety in general anxiety and other anxiety disorders, including obsessive-compulsive disorder [9, 10] and mood disorders [11, 12]. De Jong-Meyer, Beck and Riede [17] in their findings reported that individuals with higher intolerance of uncertainty have greater worry and rumination. In other words, the relationship between Intolerance of Uncertainty (IU), worry and rumination is a causal relationship. Most research in this field has been conducted on patients with anxiety (especially general anxiety disorder). For example, studies have indicated that uncertainty is the key in the explanation of concern as the main feature of the general anxiety disorder [27-29]. However, very few studies have examined IU between mood disorders. Because of the similarities and common factors between generalized anxiety disorder and depression, the question is whether the IU is also associated with depression or not. However, this has attracted a relatively less empirical interest in depression. 
Spasojevic´ and Alloy [36] postulated rumination as a mediator between cognitive risk factors/vulnerabilities and negative psychological outcomes (e.g. depression). Spasojevic´ and Alloy indicated that people with cognitive risk factors/vulnerabilities for depression (e.g. IU, self-criticism) are likely to consistently engage in rumination to cope with their negative mood. Thus, these authors conceptualized rumination as the underlying link (i.e. mediator) between cognitive vulnerability (e.g. IU) and adverse psychological outcomes. Accordingly, the purpose of this study is to present a hypothetical model and test it through Structural Equation Modeling (SEM) approach.

2. Method
The present study is a fundamental type and of a descriptive-correlational type in terms of data collection. Considering the minimum sample size required when the variables of the model (in the hypothesized model of the present study, 13 variables) ranges from 10 to 15, the sample size should be between 200 and 400 [37]. Therefore, the sample size of this study was equal to 250 subjects. To choose the subjects, by cluster sampling method, four colleges (School of Medicine, School of Paramedicine, School of Nursing and Midwifery, School of Public Health) were randomly selected. Then from each college, a number of students were randomly selected to include them in the research. 
To test the research hypotheses, the collected data were analyzed using SPSS V. 22 and LISREL 8.85 [42]. The fitness of the hypothesized model was assessed using SEM method. The data analysis was performed using the two-step approach of Anderson and Gerbing [43] as follows: in the first step, Confirmatory Factor Analysis (CFA) was used to assess the fitness of the measurement model, and in the second step, SEM was employed to assess the hypothesized structural model. 

3. Results
Table 1 presents the matrix of correlation coefficients between the variables of the research. According to the Table 1, the correlations are significant (0.549≥r≥0.357). The measurement model specifies the relationship between the observed and latent variables. The evaluation of the model was done using CFA method. The fit indices of the measurement
model (Table 2) presents a satisfactory fitness for this model. Therefore, the observed variables are capable of operating the latent variables.

 

 

 

 

In addition, assessing the structural model via the SEM method revealed that all fit indices of the hypothesized model were within the appropriate fitness range. Table 2 presents the fit indices for this model. Figure 1 depicts the hypothetical structural model with its standard coefficients. As seen in Figure 1, intolerance of uncertainty as an exogenous variable affects the rumination with a standard coefficient of 0.50. In addition, rumination affects general anxiety disorder and depression with standard coefficients of 0.72, 0.49, respectively. In the current study, the Bootstrap test was employed to evaluate the intermediate relationships. In this method, if the upper and lower limits of this test are either positive or negative, and zero is not between these two limits, then the indirect causal path will be significant. Table 3 presents the results of this test.

4. Discussion
The purpose of this study was to investigate the mediating role of rumination in the relationship between intolerance of uncertainty with symptoms of depression and general anxiety. Structural relations between the variables of the study indicate a good fit of the hypothesized model. To explain these findings, it can be said that those who have a lot of rumination, are susceptible [21] to obscure events, pessimistic forecasts and thoughts [48]. Rumination may maintain or increase the level of uncertainty. In addition, individual mental retardation, unsolved problems, and higher level of uncertainty can persist because rumination disrupts problem solving. Therefore, rumination may increase the link between uncertainty and anxiety intolerance by reinforcing and increasing distress related to uncertainty. 
Theoretically, the results of this research provide a supportive framework for Spasovich and Alvoy’s conceptual framework of rumination as interface between cognitive vulnerability and negative implications. This effect of rumination as a mediator indicates that people with a high level of uncertainty intolerance tend to chew on disturbances and disorders that worsen symptoms of anxiety and depression. In this study, uncertainty intolerance may lead to negative consequences (such as depression, anxiety) through passive 

 

 

concentration of rumination on negative experiences, which instead of active management, prolongs the stress associated with uncertainty intolerance. Perhaps, people with uncertain intolerance think that rumination will help them to better understand their feelings, gain insights and find solutions to the unknown situations they encounter.

Ethical Considerations
Compliance with ethical guidelines
All ethical principles were considered in this article. The participants were informed about the purpose of the research and its implementation stages; they were also assured about the confidentiality of their information; Moreover, They were allowed to leave the study whenever they wish, and if desired, the results of the research would be available to them.

Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors contributions
All authors contributed in preparing this article.

Conflict of interest
The authors declare no conflict of interest.



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