Structural relationship model of type D personality and depression with the mediating role of cognitive distortions and family functioning in irritable bowel syndrome patients and healthy people: A multi-group analysis

Irritable Bowel Syndrome (IBS) is one of the most common gastrointestinal disorders with symptoms of chronic abdominal pain and changes in bowel movements. Although the cause of this disorder is not known, psychological factors have been reported among the most important causes of IBS. This research was conducted to test and compare the structural relationship model of type D personality and depression with the mediating role of cognitive distortions and family functioning in patients with IBS and healthy people. Furthermore, we compared the mediational model across levels of grouping variable (IBS and healthy groups). The research method was descriptive and correlational and the sample included 236 healthy citizens, aged 20–60 years old (130 females and 100 males), who were selected by stratified random sampling method and 236 citizens with IBS, aged 20–60 years old (177 females and 59 males), who were selected by purposeful sampling method. The research participants responded to Beck Depression Inventory-short form (BDI-13), Type D Personality Scale (DS-14), Interpersonal Cognitive Distortion Scale (ICDS), Family Functioning Assessment Device (FAD), and IBS Symptom Index questionnaire based on ROME III criterion. The obtained data were analyzed using structural equation modeling (SEM). The results revealed that the model proposed in this research has an acceptable fit in both groups. Also, according to the results, cognitive distortion and family functioning play a mediating role in the relationship between type D personality and depression. In the case of comparing the mediational model across levels of grouping variable (IBS and healthy groups), we concluded that all paths are not different across the two models. In general, the findings of this study can be specifically applied by counselors and psychotherapists.


Introduction
Functional Gastrointestinal Disorders (FGID) are a group of unknown gastrointestinal diseases in which one experiences long unpredictable periods of discomfort and difficulty. Out of 25 functional gastrointestinal disorders, Irritable Bowel Syndrome (IBS) is the most common disorder (De Bortoli et al. 2018). Changes in bowel movements, pain, or abdominal discomfort without structural disorder are among the most important symptoms of IBS (Ng et al. 2018). Based on the predominant stool pattern, it includes three classes: IBS with diarrhea (IBS-D), IBS with constipation (IBS-C), and mixed IBS (IBS-M) (Kibune-Nagasako et al. 2016). The prevalence of this syndrome is 10 to 25% among the Iranian sample (Jahangiri et al. 2012); in Western countries it ranges from 10 to 20% (Saito et al. 2002) and about 11% in the world's population (Kibune-Nagasako et al. 2016). Also, this disorder is diagnosed in women 2 to 3 times more than men, and up to 80% of them experience severe IBS (Adeyemo et al. 2010). The causes of IBS have not yet been identified. However, significant hypotheses have been proposed in this regard. For example, one hypothesis states that the disorder in the brain and gastrointestinal tract interaction is involved in this disorder, suggesting the major role of the brain in the pathophysiology of this syndrome (Qi et al. 2016). Also, psychiatric disorders are highly associated with IBS and depression is among the most important ones (Lee et al. 2017a). Many patients with IBS experience major emotional disorders, particularly depression (Qi et al. 2016).
In 2015, the number of depressed people in the world was estimated at 4.4% and the total number of depressed people increased by 18.4% from 2005 to 2015, suggesting a general increase in the prevalence of this disorder (World Health Organization 2015). Based on Diagnostic and Statistical Manual of Mental Disorders-Version Five , if a person has the following symptoms, he/she will be diagnosed as a depressed person: Feeling sad or having a depressed mood, loss of interest or pleasure in activities once enjoyed, changes in appetite -weight loss or gain unrelated to dieting, trouble sleeping or sleeping too much, loss of energy or increased fatigue, increase in purposeless physical activity or slowed movements or speech, feeling worthless or guilty, difficulty thinking, concentrating or making decisions and thoughts of death or suicide (American Psychiatric Association 2013).
Chronic diseases and a combination of genetic, biological, psychological, social, and environmental factors have been proposed in the etiology of depression (Mooney and El-Sayed 2016). Moreover, personality types are a special and important factor in the formation of abnormal reactions and mental disorders (Al-Qezweny et al. 2016). One of the personality types associated with depression is Type D personality, which includes two major components: negative affectivity (NA) and social inhibition (SI). In a negative affectivity trait, the person tends to experience increasingly negative emotions such as anxiety, depression, and hostility. In a social inhibition trait, the person is unwilling to express emotions due to fear of being rejected and having a low level of selfesteem (Yilmaz et al. 2016). Type D personality was introduced by Denollet et al. (1995) as a disturbed and anxious personality type. Based on early estimates, this personality type is common in 20% of the general population (Allen et al. 2019;Denollet 2005). Type D personality is identified when people score above a predetermined cut-off on both the NA and SI subscales of the DS14 (Lambertus et al. 2018). Type D displays special traits that negatively influence people's health (Williams et al. 2016). Also, according to the existing studies, this type predicts poor physical health and poor public health (Allen et al. 2019;Kupper and Denollet 2018a) and is considered a risk factor for mental disorders, especially depression (Lambertus et al. 2018). People with this personality type show a higher level of harmful behavior and perception compared to others (Cheng et al. 2018).
Although trait psychological features are supposed to be stable over time, in case of Type D, there are some evidences which lead to its poor temporal stability over time. Ossola et al. (2015) suggested that NA and depression are overlapping constructs, and DS14 measures the features causing depression rather than a personality disposition. Based on Ossola et al.'s (2015) results, it can be concluded that NA may not be the stable personality trait as it has been claimed to be, but could be considered as a psychological trait. Regarding the operationalization of type D, following Lodder (2020), it can be considered that SI or NA can separately produce Type D personality effects even if only one of them (NA or SI) is related to the outcome.
In a one-year follow-up study of heart failure patients, these patients displayed distinctive personality trait D that was independently associated with the severity of depression symptoms (Burkauskas et al. 2015). Also, previous studies have shown that higher levels of negative affectivity and social inhibition are associated with more depressive symptoms (Gupta and Basak 2013;Van Dooren et al. 2016). Moreover, type D personality affects a construct called cognitive distortion. In this construct, the information processing activity of individuals is disrupted or inactivated, and then, misconceptions guide the person's behaviors (Ota et al. 2020). So, in response to environmental events, people display behaviors and emotions that are the result of spontaneous and automatic thoughts (Rnic et al. 2016). These thoughts include dichotomous thinking, fortune telling, over-generalization, mind reading, discounting positive aspects, emotional reasoning, labeling, personalization, magnification or minimization, blaming, should statements, jumping to conclusions, what if, selective abstraction, and an unfair comparison.
Early studies on cognitive distortion have focused on depression and based on the findings of such studies, cognitive distortions are more common in depressed people than in healthy ones. Cognitive distortions are considered as one of the features of depression disorder (MacLaren et al. 2015). When one's major negative beliefs begin to work and spontaneous negative thoughts appear, a natural, negative, neutral, or even positive event can influence negative affectivity (a type D dimension) and abnormal behaviors. Therefore, type D personality can be associated with depression due to cognitive distortion.
Moreover, cognitive distortions are formed in the context of interpersonal relationships, which is a part of social interactions, depending on the role of family and its function. According to World Health Organization (WHO), the family is the primary social factor that brings health and well-being for people. When families are threatened, they experience imbalance due to morbid behaviors. Family functioning, which is the joint effort of the members to maintain balance in the family, is of crucial value in this regard. If people's communication and tendencies are based on intimacy, understanding, and affection, all members will be less harmed by the pressures of illness and difficulties of life (Song et al. 2019). Based on different studies, the family functioning of depressed patients has some defects and abnormalities that play a role in the occurrence of this disorder and affect the treatment outcomes. Wiegand-Grefe et al. (2019) found that family functioning is an important mediator in the development of mental disorders in parents, which in turn affects the development of the children. On the other hand, some studies addressed the association between type D personality and family functioning. For instance, Spek et al. (2018), revealed that participants with Type D and participants with high NA tend to experience less social support and less relationship adjustment (the variables related to family functioning). Likewise, they reported an association between Type D personality and more loneliness, lower social support and relationship adjustment in people with diabetes. Other studies also provided some evidence linking Type D personality with less social support in individuals with coronary heart disease and patients with type 2 diabetes mellitus (Ginting et al. 2016;Shao et al. 2017).
In general population, studies indicated that there was a significant relationship between Type D personality and physical symptoms, which was mediated by subjective stress and anxiety (Kupper and Denollet 2007;Smith et al. 2018). Mols and Denollet (2010), in a review study, revealed that Type D characteristics had a negative impact on mental health status (more symptoms of depression, anxiety, post-traumatic stress disorder, mental distress, passive coping, and less social support) and physical health status (more somatic complaints, lower health status, and more influenza-like illness reporting) in the general population. The relationship between type D and depression seems to be influenced by other variables and populations as well. For instance, several studies have showed an association between type D and depression in patients with chronic heart failure (Kupper and Denollet 2018b;Schiffer et al. 2008;Widdershoven et al. 2013). Type D personality seems to confer a specific vulnerability to chronic stress, and it has been associated with low subjective and physician-assessed health ratings (Chapman et al. 2007). Irritable bowel syndrome (IBS) patients frequently experience psychological disorders, such as depression and anxiety. Lee et al. (2017b), in a systematic review and meta-analysis, showed depression and anxiety levels are higher in IBS patients than in healthy controls. Several studies have been conducted investigating the role of personality traits in IBS. Rafezi et al. (2018) conducted a cross-sectional analytical study on 100 healthy and IBS people. They compared the personality traits of 50 individuals diagnosed as IBS patients and 50 healthy individuals. According to their results, people with IBS had higher neuroticism and lower extraversion than healthy people, both of which are associated with type D characteristics (De Fruyt and Denollet 2002). Hence, some personality traits are closely associated with IBS. Sibelli et al. (2016) showed a significant relationship between anxiety and depression and an increased risk of IBS. Therefore, the role of depression as a risk factor for IBS can also be significant. Based on the tradition followed by previous studies, the present study intended to examine the structural relation between type D personality and depression with a mediating role of cognitive distortions and family functioning both in people with IBS and healthy people. Furthermore, we compared the two mediation models across levels of grouping variable (IBS and healthy groups). The suggested hypotheses are as follow: Hypothesis 1: There is a structural relation between type D personality and depression with a mediating role of cognitive distortions and family functioning both in people with IBS and healthy people. Hypothesis 2: There is a significant difference between the paths across the two models people with IBS and healthy people.

Method
The researchers adopted a descriptive and correlational approach in order to conduct the study. Its population included healthy people and people with IBS in Bandar Abbas, Iran. A total of 472 people participated in this study, of which 177 (75.2%) female and 59 (24.8%) male samples were included in the IBS group and 130 (55.2%) female and 106 (44.8%) male samples were included in the healthy people group. The total group also included 307 females (65%) and 165 males (35%). 236 healthy citizens were selected using a stratified random sampling method. Their age range was 20-60 years old whose mean and standard deviation were 38.37 and 2.54, respectively, and the 236 citizens with IBS, who were selected using a purposeful sampling method. Their age range was 20-60 years old whose mean and standard deviation were 39.62 and 2.39, respectively. To determine the patients with IBS, the IBS Symptom Index Questionnaire was used based on the ROME III criterion. ROME III criterion applied to detect the presence of IBS was lower abdominal pain or discomfort in association with an alteration in bowel habit, and having no organic GI disease. People who had symptoms of the disorder and a history of visiting a physician for the mentioned problem, according to this questionnaire, were diagnosed as IBS cases. After selecting the participants, they were provided with a brief explanation of the research objectives and were ensured about their right to leave the study at any stage.
Informed consent was obtained from all individual participating in the study. Once the participants filled the consent forms, they were asked to complete the questionnaires.

Research Tools
Beck Depression Inventory-Short Form  This questionnaire has 13 items, including two subscales i.e., the negative affectivity (items 1, 2, 3, 4, 5, 6, 7, and 10) and anhedonia (items 7, 8, 9, 11, 12, and 13). The goal of this questionnaire is to assess one's depression and a high score indicates severe depression. Luty and O'Gara (2006) reported Cronbach's alpha of this scale at 0.88, and its concurrent validity (correlational coefficient) compared with the Montgomery Asberg Depression Rating Scale, was 0.76. In this study, the reliability of the negative affect and anhedonia subscales by Cronbach's alpha method was estimated at 0.79 and 0.78, respectively.

Type D Personality Scale (DS-14)
This scale was developed by Denollet (2005) to identify people with type D personality. It has two subscales of negative affect (items 2, 4, 5, 7, 9, 12, and 13) and social inhibition (items 1, 3, 6, 8, 10, 11, and 14). The Type D Personality Questionnaire consists of fourteen 5-point Likert questions (incorrect, somewhat incorrect, no idea, somewhat correct, and correct), with a score above the cutoff (≥ 10) on both measures indicating a type D personality. The reliability of this scale in Belgium was reported at 0.81 and its validity was reported at the desired level. So, the negative affect subscale was correlated with the Neuroticism subscale of the Big Five Factors Scale (at a significance level of 0.001). Factor analysis of Persian version of DS14 yielded the two-factor structure in MI patients and test-retest stability of the NA and the SI subscales were 0.86 and 0.77, respectively over a 2-month period (Bagherian and Ehsan 2011). Social inhibition subscale is negatively correlated with extraversion (−0.61) and level of consciousness (−0.40), and positively correlated with neuroticism (Denollet 1998). In Iran, based on the calculation of Cronbach's alpha, the reliability of this tool was estimated at 0.86 (Fakhari et al. 2015). Moreover, the reliability of the NA and the SI subscales in the present study was estimated at 0.81 and 0.81, respectively.

Interpersonal Cognitive Distortions Scale
The purpose of this scale was to assess the level of cognitive distortion in people. It was designed by Hamamci and Büyüköztürk (2004). This 19-item scale includes three subscales of rejection in interpersonal relationships, unrealistic expectations in interpersonal relationships, and misperceptions in interpersonal relationships, scored on a five-point Likert scale. They are scored with numbers 1, 2, 3, 4, and 5, respectively. A high score indicates high cognitive distortion in the person and a low score indicates low cognitive distortion. The reliability of the questionnaire through internal consistency by Cronbach's alpha and test-retest with a two-week interval for the whole scale was obtained at 0.67 and 0.74, respectively (Hamamci and Büyüköztürk 2004). They also calculated these factors at 0.73 and 0.70 for the subscale of rejection in interpersonal relationships, 0.66 and 0.76 for unrealistic expectations in interpersonal relationships, and 0.73 and 0.70 for misperception in interpersonal relationships, respectively.
Its validity was calculated at 0.45, 0.53, and 0.53, respectively, through correlation with the scale of irrational beliefs, the scale of automatic thoughts, and the scale of the tendency to conflict in interpersonal relationships (Hamamci and Büyüköztürk 2004). In Iran, the construct validity of the questionnaire and the existence of three factors of rejection in interpersonal relationships, unrealistic expectations in interpersonal relationships, and misperception in interpersonal relationships were confirmed. Cronbach's alphas for the subscale of rejection in interpersonal relationships, unrealistic expectations in interpersonal relationships, and misperception of interpersonal relationships were obtained at 0.79, 0.82, and 0.81, respectively (Esmaeelpoor et al. 2015). In the present study, Cronbach's alpha for the subscale of rejection in interpersonal relationships, unrealistic expectations in interpersonal relationships, and misperception of interpersonal relationships was estimated at 0.78, 0.81, and 0.81, respectively.

Family Functioning Assessment Device (FAD)
The purpose of this scale is to assess family functioning. It was designed based on the McMaster model of family functioning. It has seven components including problem-solving, communication, roles, affective involvement, affective responsiveness, behavior control, and general family functioning. In this study, in order to assess family functioning, the general family functioning components (questions 7, 14, 21, 28, 35, 36, 39, 43, 47, 50, 52, and 53) were used. A high score indicates the desirable general family functioning and a low score indicates poor functioning. According to Epstein et al. (1983), the minimum alpha coefficient of scales was 0.75. In Iran, Yoosefi (2012) identified three structures in this test by using factor analysis: family roles, problem-solving, and expression of affections. In the present study, the reliability of this scale with Cronbach's alpha method was estimated at 0.75.

IBS Symptoms Index Scale Based on ROME III Criteria
The purpose of this scale is to diagnose people with IBS based on ROME III diagnostic criteria. This scale includes 10 questions regarding the severity and frequency of IBS symptoms. This scale is completed by a specialist physician. The reliability coefficient of this scale using Cronbach's alpha was estimated at 0.63 (Kanazawa et al. 2015) and its Cronbach's alpha was estimated at 0.73 in the present study.
Statistical Analysis Statistical analysis was performed using SPSS (version 26) and AMOS (version 24) software. The models were fitted using structural equation modelling and a Maximum Likelihood Estimator. The criteria for evaluating model fit include Chi-square divided by the degrees of freedom (χ2/df), Comparative Fit Index (CFI), the Tucker-Lewis Index (TLI), and Root Mean Square Error of Approximation (RMSEA). The χ2/df was recommended with values of 5 or less (Hu and Bentler 1999), for both the TLI and CFI, we considered the values above 0.90 to indicate adequate fit (Hu and Bentler 1999), and for the RMSEA, the values above 0.10 were considered as unacceptable and values below 0.06 as good model fit (Chen et al. 2008).
Also, we conducted multivariate normality test in AMOS, by the calculation of Mardia's coefficient, which is a multivariate measure of kurtosis. This test is highly sensitive to sample size, with larger sample sizes being more likely to produce significant (non-normal) results. Therefore, according to Stevens (2012), it was used in conjunction with the kurtosis values for individual variables. Kurtosis values above 3 (in magnitude) may designate that a variable is not normally distributed (Westfall and Henning 2013).
Since Type D personality is hypothesized to constitute a statistical interaction between the construct's two subcomponents (NA and SI), in line with recommendations by Lodder et al. (2019), we used the matched product indicator (Matched PI) as the interaction method and run the model. We first ranked the items in terms of reliability, then multiplied items with similar ranking and got the seven interaction items. Before multiplying the items, we mean centered the items as well. Accordingly, we tested two models as follow: 1-A SEM with NA and SI as exogenous (independent) latent variables, cognitive distortion and family function as mediators and depression as criterion (dependent) variable. 2-A SEM with NA, SI and NA*SI (interaction effect) as exogenous (independent) latent variables, cognitive distortion and family function as mediators and depression as criterion (dependent) variable.
For multi-group analysis, we used the manage groups function in the AMOS software to compare path coefficients in both IBS and healthy models. For this purpose, each path was named twice with different labels for both groups. We initially selected Critical ratios and subsequently the difference in the Analysis Properties in order to compare coefficients for the specified paths in both groups in the output. It yields a z-test for the difference between coefficients from IBS Model to Healthy Model, and for a two-tailed test, if this value is greater than |1.96| (absolute value of 1.96) for the difference between paths to be statistically significant at p < .05. This method produces only one set of fit statistics for overall model fit. Table 1 shows the mean and standard deviation of the research variables in the IBS and healthy groups.

Results
The multivariate normality of the scores of the research variables in the IBS and healthy groups was examined through multivariate measures of skewness and kurtosis and the results confirmed the data normality. The result of normality test had been provided as a supplementary file. As mentioned earlier, we tested two models and reported the model fit indices related to each model, unstandardized and standardized direct effects for both groups in Table 2. Table 2 shows model fit indices and structural regression coefficients for the two models in IBS and healthy groups. Both models resulted in a χ2/df value lower than 5, a sign of good model fit. According to the RMSEA, CFI and TLI, the models fitted the data best. Both Models 1 and 2, showed RMSEA 95% confidence intervals lower than 0.06. According to both CFI and TLI, models 1 and 2 showed good fit with values of approximately 0.90. According to the results, the models 1 and 2 were well-fitted in both groups.
The results of the Hayes PROCESS macro for mediation method in IBS model indicated that the indirect path coefficient between type D personality and depression through cognitive distortions was significant (indirect coefficient = 0.11, 95% CL = [0.12, 0.26]) and the indirect path coefficient between type D personality and depression through family functioning was statistically significant (indirect coefficient = 0.08, 95% CL = [0.03, 0.13]) as well. Furthermore, the results of the mediation analyses in healthy model indicated that the indirect path coefficient between type D personality and depression through cognitive distortions was significant (indirect coefficient = 0.13, 95% CL = [0.07, 0.20]) and the indirect path coefficient between type D personality and depression through family functioning was statistically significant (indirect coefficient = 0.13, 95% CL = [0.007, 0.21]). Considering all these results, the relationships between type D personality and depression was significantly mediated by the cognitive distortions and family functioning in the two groups.
One of the purposes of the present study was to compare path coefficients in both IBS and healthy models. In addition, model coefficients were compared using multi-group analysis in AMOS software. The results showed that all path coefficients were not different in the two models. According to the results, the z-value for all comparisons was not exceeding the critical value of |1.96|. Consequently, we have no evidence to suggest that these paths are unequal across the two models. Table 3 summarizes the multi-group analysis results.

Discussion
The first aim of the present study was to investigate the Type D personality and depression relationship mediated by cognitive distortions and family functioning in two IBS and healthy groups. Lodder (2020) provided the first empirical support to show that false positive Type D personality effects may occur even if only one of the personality traits (NA or SI) is related to the outcome. Accordingly, in some studies conducted in the last decade, Type D personality effects were estimated based on the main and interaction effects of the continuous NA and SI scores. Following Lodder (2020) and in line with Ossola et al. (2015), we analyzed the two models so as to test the main and interaction effects of the continuous NA and SI scores. The results revealed that the models 1 and 2 were well-fitted. In model 1, we investigated the relationship of NA and SI with depression mediated by cognitive distortion and family function. In model 2, we tested the relationship of NA and SI and NA*SI (interaction effect) with depression mediated by cognitive distortion and family function as mediators as well. Lodder (2020) stated that if NA and SI sum scores are both independently related to an outcome, there is an additive Type D effect and there is a synergistic Type D effect when there is a significant interaction between NA and SI in the same direction as the main effects. In the current study, both NA and SI are independently important in explaining variance in depression, but the effect of these two personality traits is not more than the sum of their parts. Since our results indicated an additive effect, we concluded an additive Type D effect. Furthermore, the findings demonstrated a significant relationship between type D (NA and SI effects) and depression in addition to cognitive distortions and family functioning, on the one hand, and cognitive distortions and family functioning with depression, on the other hand, for both healthy people and IBS patients. The results revealed no significant association between NA*SI and depression and NA*SI and cognitive distortion in IBS group. Furthermore, the results indicated no significant association between NA*SI and depression, NA*SI and cognitive distortion and NA and family function in healthy group.
The present study further aimed at assessing whether healthy people differ from people suffering from IBS in the extent to which family functioning and cognitive distortion mediate the relation between Type D personality and Depression. We have no evidence to suggest that these groups are different in this regard. Although we expected a significant difference between the path coefficients in the two models of healthy individuals and patients, the results did not support this anticipation. It seems that other variables such as IBS subtypes, disease severity, comorbidity of psychological disorders and physical illness can be considered as possible explanations for this nonsignificant difference and should be evaluated in prospective studies. Our results represented that the proposed models have a good fit in both healthy and IBS groups, which is consistent with the results of previous research (Al-Qezweny et al. 2016;Gupta and Basak 2013;Kibune-Nagasako et al. 2016;Lee et al. 2017a). Individuals with type D personality tend to experience negative emotions and avoid being in the community and expressing their feelings and are more prone to mental health problems and disorders such as depression and psychosomatic illnesses (Williams et al. 2016).
Further, those with type D personality experience depression and low general health, along with disrupted interpersonal relationships, due to the combined effects of negative excitement and social inhibition (Van Dooren et al. 2016). It seems that type D personality can lead to cognitive distortions in people because of disturbing their emotions and creating a negative attitude toward themselves, and these cognitive distortions, in turn, can cause depression.
Our findings suggest that cognitive distortions and family functioning may mediate the relationship between Type D personality and depression. Since the direct effects of NA/SI on depression remained statistically significant when we included the mediators in the model, there was a partial mediation effect. On the other hand, a complete mediation effect can be concluded if the direct effect of NA/SI on depression turns nonsignificant after including the mediators in the model. Subsequently, the cognitive distortions and family functioning do not fully, but partially, mediate the additive Type D effect on depression. Depression is a disorder that may stem from problems with emotional regulations (Gilbert 2012;Pereira et al. 2015;Sheeber et al. 2009). Furthermore, people with type D personality have probably no proper emotional regulation due to poor family functioning, which can lead to depression in these people. Moreover, they may hide their feelings and emotions because of difficulties in expressing love due to lack of appropriate words, friendly attitudes, and physical contact. Additionally, the negative emotion and social restraint of type D personality can increase depression given the fact that families do not allow their children to express their thoughts and feelings, disagreements between family members are not considered normal, and negotiations for resolving disputes are not conducted by agreement. Similarly, improper family functioning can contribute to stress and thus depression. According to previous research studies, interactions between biological, personality, and stressful life events may increase the likelihood of experiencing depression (McLeod et al. 2007;Pereira et al. 2015). In addition, various family factors are associated with the risk of depression. For example, parental psychological pathology, parental cognitive style, family emotional climate, parenting style, attachment, and parental conflicts are among the factors that may be possible mechanisms for experiencing depression. However, no study has so far thoroughly elucidated the mechanism by which dysfunctional family interactions may increase a person's vulnerability to depression. The evidence indicates that psychosomatic illnesses can both act as an antecedent to mental disorders and occasionally as a consequence of these disorders. Therefore, people with IBS, similar to other psychosomatic illnesses, are prone to develop more cognitive distortions, and stronger cognitive distortions may result in longer depression. In addition, these individuals have a more disproportionate family functioning compared to normal people. According to the results of previous studies, poor family functioning can lead to more depressive experiences (Ghamari 2012;Pereira et al. 2015).
In general, the results of the present study demonstrated that type D personality has a positive relationship with depression under the influence of irritable bowel syndrome, and cognitive distortion and family functioning mediate this relationship. However, the correlational nature of our study prevents us from reaching a causal conclusion. The correlation coefficients are significant despite their small size. It can be one of the limitations of the study and we suggest to include more relevant variables like anxiety, social support, and wellbeing in the model in future studies.
The observed relationship between Type D personality and depression through cognitive distortion and family functioning confirmed the need for paying more attention to personality traits and family climate in order to prevent mental disorders. Furthermore, the interaction of these variables with psychosomatic disorders is considered as an important factor that should be taken into account in disorders such as depression.
Despite the above-mentioned points, this study has several limitations that should be considered in generalizing the findings. As it was mentioned earlier, the lack of causal conclusion due to the correlational type of the research and the lack of examining the interaction between the subjects' gender, occupation, level of education, and socioeconomic status with the studied variables are the most important limitations of the present study. Thus, it is suggested that future studies test the proposed model on the other populations of psychiatric patients by considering the mediating or moderating effects of such demographic variables. It is further suggested that educational programs for IBS patients pay special attention to these individuals' disease and control it through designing and using psychological therapies, and in general, nonpharmacological and cultural strategies in order to help patients and inform them about their disorder. a z-score greater than or equal to the critical value of 1.96 is significant