This research is quasi-experimental in which the pretest-posttest control group design was used. Independent variable in this study was treatment (acceptance and commitment therapy and cognitive behavioral therapy) and dependent variable was, changes in social phobia inventory (SPIN) scores as a result of the application of two different treatment methods.

The statistical population consisted of all undergraduate students of Islamic Azad University of Marvdasht and Shiraz, in 2016.

The sampling was done in two stages: in the first stage, 470 students were selected by convenience method. Students who got high scores in SPIN (35-40 or higher) were identified and were clinically interviewed (according to the criteria of the Diagnostic Statistical Manual, Fifth Edition). The criteria for entry to the experimental group were: studying in university, not taking psychiatric drugs, not having other psychological and personality disorder, not participating simultaneously in other therapy programs and not receiving individual or personal counseling. Exclusion criteria were active suicidal ideation, severe depression, history of bipolar disorder or psychosis, substance abuse or dependence within the last 6 months. Upon identifying students with social anxiety disorder and receiving the final consent of the individuals to participate in the research, in the second stage of sampling, 45 students with social anxiety disorder were randomly assigned to three groups as follows: 15 in the experimental group ACT and 15 in the experimental group CBT and 15 were assigned into control group.

All three groups were assessed prior to treatment (Pre), by social anxiety inventory (SPIN) [36]. Then one of the experimental groups received CBT based on Hoffman & Otto’s practitioner’s Guide [5], and the second experimental group received ACT based on the Eifert and Forsyth practitioner’s Guide [23]. For twelve weekly, 2-hour, group therapy sessions1 but the control group did not receive any intervention. At the end of treatment, the subjects in all groups completed the social anxiety inventory (SPIN) again in the post-test stage and finally the obtained data was analyzed by covariance analysis method (Table 1).

Table 1: Summary of treatment sessions.

It should be mentioned that the control group had already been informed about the necessity of receiving treatment, after post assessment, they were offered treatment free of charge, and were able to choose either CBT or ACT at the end of the research project.

The amount of social anxiety was measured by social anxiety inventory (SPIN), which is a self-assessment scale of 17 items and total scores can range from 0 to 68. SPIN was designed by Canner et al. in 2000 to assess social anxiety and it’s very sensitive to reduction of the symptoms of social anxiety over time. One of its uses is to test the response to treatment in social anxiety disorder. It is a useful screening tool for distinguishing between people with and without social anxiety, scores above 51 are considered very severe social anxiety and scores between 41 to 50 moderate, 21 to 30 low and less than 20 normal, the cut point 40 with an accuracy of 80% can distinguish people with or without Social phobia [36]. Results from the original validation study suggest that the SPIN possesses strong internal consistency, test–retest reliability, convergent validity, discriminative validity, construct validity, and sensitivity for measuring change following pharmacological treatment [37].

The assumptions of covariance analysis, the final analysis results are Covariance analysis was used to analyze the data and compare the experimental and control groups. By confirming presented in Table 2.

Table 2: Covariance analysis.

As shown in Table 2, the value of F for the difference between the groups (control and experiment) is significant at the significance level of ≤ 0.001. This means that there is a significant difference (with pre-test factor control) between the social anxiety scores of the experimental and control group. Therefore, it is confirmed that therapy sessions have been effective. Another indicator to be considered is the effect size, which is indicated in the table as “ETA”. The value of ETA squared is 0.372, which in percentage will be 37%, meaning that 37% of the changes in social anxiety scores are due to the implementation of the treatment.

Subsequently, the difference between pairs of groups was investigated using post hoc test. The results of the follow-up test are presented in Table 3.

Table 3: Post-test results.

The results of the post hoc test in Table 3 show that there is a significant difference between the control group and the CBT group, as well as between the control group and the ACT group at a meaningful level of ≤ 0.001, and both therapeutic methods have been effective. Although the effect ACT was slightly higher than CBT, but the difference between the two treatment groups was not significant.

The aim of this study was to compare the effectiveness of cognitive behavioral group therapy and Acceptance and commitment group therapy in reducing the social anxiety symptoms in students with social anxiety disorder. The results showed that both approaches reduced the social anxiety symptoms compared to control group. Initially, in order to determine the effectiveness of each approach separately, it can be said, based on literature, that the results obtained using ACT approach [38,39] were consistent with the results obtained using CBT approach [16,40,41].

The findings of the present study were consistent with the findings of study carried out by Forman, Herbert, Moitra, Yeomans, and Geller [33] which compared the effects of ACT and CBT approaches in outpatients with moderate to high levels of depression and anxiety without being diagnosed with depression and anxiety; while they were inconsistent with the study carried out by Lappalainen et al. [42] which studied only 28 patients with different disorders individually treated by different therapists and indicated that the symptoms reduced more significantly in patients treated with ACT than in patients treated with CBT. Although, in the present study, the symptoms of social anxiety reduced more significantly in ACT group than in CBT, but the difference was insignificant. These are consistent with the findings of following studies: Arch et al. [34] compared the effectiveness of ACT with CBT on a sample population of individuals with anxiety disorders; Craske et al. [3] investigated the interventions and consequences of cognitive behavioral therapy and Acceptance and commitment therapy in treatment of social anxiety disorder; Kocovski, Fleming, Hawley, Huta and Antony [43] compared acceptance and commitment group therapy with cognitive behavioral group therapy on social anxiety. In order to further clarify the findings, we can mention the similarities between the two approaches and common processes and methods in these two approaches including that both approaches provide a context which identify the cognition as the product of a system rather the expression of internal truth; both approaches believe in inefficiency of automatic, inflexible responses to experience which enforces the problems [31]. The other common feature in these approaches is exposure to stressful thoughts rather controlling or suppressing them, which is considered to be the main treatment factor in the model Hofmann and Otto model [37] used in this research, though with a different logic and different methodology; in CBT, exposure takes place with the aim of reducing anxiety and gaining control over fear, anxiety, evaluating the individuals’ catastrophic predictions [44] and avoiding social situations is considered to maintain anxiety [37]; but in ACT, the aim of exposure to or experiential acceptance which is studied as a change mechanism [32] is to increase the individuals’ interest in experiencing internal incidents as they are accomplishing what is of value to them in life and what is consistent with their life values [43]. In the present study, one important intervention in therapy sessions for both experimental groups were exposure. Given the potential of exposure in treating the anxiety disorders (For example, Norton, Price, [45], it is possible that this shared treatment component counterbalances the differences in two approaches and leads to equal effectiveness in both therapies. Furthermore, in a study carried out by Burton, Schmertz, Price, Masuda, and Anderson [46] on the relationship between mindfulness and fear of negative evaluation in CBT therapy on social anxiety disorder, it was shown that although the mindfulness is associated with the fear of negative evaluation as a main factor of social anxiety disorder, better mindfulness did not moderate treatment outcome. The findings confirmed the aforesaid results given that mindfulness is an important factor in ACT therapy [47].

Moreover, several authors have suggested that exposure and cognitive restructuring are difficult to differentiate both conceptually and practically, since both specifically aim to provide new learning experiences that contradict patients’ beliefs about the likelihood and cost of negative social outcomes [37,48]. Exposure has been shown to lead to cognitive change [49], and cognitive techniques, especially behavioral experiments, often involve exposure-like experiences. In addition, ACT emphasizes eliminating tendencies to avoid or escape from unpleasant emotions and an emphasis on tolerating unpleasant feelings which is so similar to what exposure asserts. Based on this once more we can conclude that a similarity of these two approaches can lead to similar results.

However, the findings in literature are inconsistent. For example, Kocovski, Fleming, Hawley, RingoHo, Antony [43] questioned whether, in social anxiety disorder, cognitive reappraisal is considered to be the unique mechanism of change in Cognitive Behavioral Group Therapy and mindfulness and acceptance in Mindfulness and Acceptance-based Group Therapy? Cognitive reappraisal was reported to be effective only in cognitive behavioral group therapy while mindfulness and acceptance were an effective mechanism in both therapies.

While there have been many studies on the effectiveness of each approach on various disorders individually, for example, Bluett, Homan, Morrison, Levin, and Twohig, [50] reported that ACT as the effective therapy on anxiety disorders, but lack of studies comparing the effectiveness of these two approaches on a specific disorder is considered to be the limitation of the present study. Also, the sample population entirely consisted of university students which are considered to be a specific population which in turn limits the potential of generalizing the results to other populations; accordingly, it is suggested that other populations also be used in future studies. Lack of facilities for at least 3-month follow-up is also another limitation of the study and hence it cannot be determined whether these two approaches are equally effective in reducing the symptoms of social anxiety disorder and the results obtained will remain stable. It is possible to obtain different results by extensive research and follow-up as Arch et al. [34] indicated after a 12-month follow-up that the symptoms of social anxiety are reduced more significantly in ACT group compared to CBT group.

The aim of present study was to compare the effectiveness of cognitive behavioral group therapy and acceptance and commitment group therapy on reducing of social anxiety symptoms in university students with social anxiety disorder. The findings showed that the two therapeutic approaches were equally effective in reducing the symptoms of social anxiety in university students. While acceptance and commitment group therapy, slightly outperformed the cognitive behavioral group therapy in the treatment of social anxiety disorder in university students, still further studies in this area is needed to come up with more clear result.

We, the authors recommend that the same study replicated with different population in order to find out whether the result obtained will be of any dereference.