norton and hope ( 2 ) noted that this problem was related to the dissemination of effective treatments and accessibility to effective treatments . the cognitive behavioral approaches have published many therapeutic manuals and protocols for emotional disorders and their effectiveness have been confirmed by many studies ( 1 ) . using these treatments face to two great obstacles including lack of access to these treatments by the clients and the lack of applying these treatments through therapists ( 3 ) . lifetime prevalence of anxiety disorders and depressive disorders has been reported respectively , 29 % and 21% ( 4 ) . these disorders associated with considerable burden on the societies directly and indirectly ( 5 , 6 ) . comorbidity between these two disorders has been reported about 40% 80% and they have high comorbidity with other disorders such as drug abuse . these chronic disorders have the risk of relapse , recurrent and low chance for improvement without treatment ( 7 ) . although current cognitive therapies have been found successful in improving emotional disorders , they have some limitations such as loss of response to the current therapies among patients ( 8) . in addition however , different therapeutic instructions have been published for disorders , training and obtaining skills in each of them need to spend money and time . moses and barlow ( 8) suggested that the solution for these problems was to create a unified therapeutic approach for a range of emotional disorders . unified approach or cognitive - behavioral transdiagnostic therapy is a therapy that has the same therapeutic principals for all emotional disorders without any adaptation to the especial disorder ( 9 ) . remarkable attention has been devoted to the transdiagnostic therapy that has been newly practiced ( 1012 ) . the transdiagnostic therapies have been shown their effectiveness in the treatment of wide variety of emotional disorders ( 9 , 12 , 13 ) . in the area of cognitive behavioral transdiagnostic treatments , the current study was examined the effectiveness of transdiagnostic group therapy in reduction of sub - clinical symptoms of anxiety and depression and compares it with classical cognitive group therapy . this study was a comparative or relative efficacy study that compared two therapeutic models with each other based on the outcomes scales instead of comparison of the one therapy with a control group without any intervention or in the waiting list . as we know , the cognitive therapy is a common and useful intervention ( 14 ) and a standard treatment was considered for one of the control groups . forty one participants ( in tow groups ) were enough to gain appropriate statistical power for testing hypotheses . people with inclusion and exclusion criteria were selected and assigned randomly to experimental and control groups . this study was carried out in akhavan hospital , tehran iran during may and june 2011 . the inclusion criteria included as anxiety and depressive symptoms based on the cut - off of 18 and higher in the depression subscale and score of 16 and higher in the anxiety subscale of the depression , anxiety , and stress scale ( dass-42 ; 20 ) . these cut - offs were determined based on the lovibond and lovibond s ( 15 ) method that used percentage points for determination of severity levels . according to this matter , the percentage points of 78 and higher formed low level of severity . the exclusion criteria was based on the axis i disorders , including anxiety disorders , depression , psychosis , psychosomatic and drug abuse , by using the anxiety disorders interview schedule for dsm - iv ( adis - iv ) . participants who obtained a score equal to or greater than 18 in depression subscale and 16 in subscale of anxiety evaluated based on the anxiety disorder interview schedule for dsm - iv in order to determine inclusion and exclusion criteria . then , we explained the study , its conditions , and moral status to them and got the informed consent , after that the study instruments were administrated and readministered after treatment sessions . the study administrated on the students population of universities across tehran city . among all prepared participants , only data of 33 students analyzed after the end of invention . 16 students assigned at control group ( cognitive group therapy ) , and 17 students in transdiagnostic group . the mean ( standard deviation ) age of the participants was 22.6 ( sd=3.1 ) . results showed that experimental group s age with mean ( standard deviation ) of 22.88 ( 1.62 ) and control group mean ( standard deviation ) of 23.75 ( 2.75 ) statistically not significant ( m= 0.87 ; sd= 0.77 ; t= 1.12 ; p < 0.27 ) . in addition , differences between genders in two group not statistically significant using chi square test ( x=0.24 & p < 0.62 ) . the participants filled out demographic and informed consent at intake . they participated in the group cognitive therapy ( 16 ) and transdiagnostic group therapy ( 17 ) for 8-sessions per week ( a two - hour session ) . sessions content , procedures , and techniques were based on the published and known therapeutic instructions ( 16 , 17 ) . two absent sessions was permissible and three absent sessions was considered as drop - out . the anxiety disorders interview schedule for dsm - iv ( adis - iv ; ( 18 ) ) , is a semi - structured diagnostic interview designed to assess the presence , nature , and severity of dsm - iv anxiety , mood , and somatoform disorders , as well as previous mental health history . the interview also contains a brief screen for psychotic symptoms , and alcohol and substance abuse . all adis - iv interviewers , advanced doctoral students , were trained to rigorous standards for reliability with an expert adis - iv interviewer . this measure has demonstrated acceptableto excellent interrater reliability for the anxiety and mood disorders ( 19 ) . the depression , anxiety , and stress scale ( dass;(15 ) ) is a 42-item self - report measure in which participants rate the frequency and severity of experiencing negative emotions . the dass is comprised of three subscales , physical symptoms of anxiety ( dass - a ) , mental stress ( dass - s ) , and depression ( dass - d ) . each of 42 symptoms is presented as an item , and is rated on a 4-point frequency and severity scale . internal consistencies for all three factors were in the very good to excellent range ( dass - d 0.91 ; dass - a 0.84 ; dass - s 0.90 ) . the depression , anxiety and stress subscales have shown strong psychometric properties with a range of populations ( 15 , 21 ) . they were reported good internal validity for depression ( 0.77 ) , anxiety ( 0.79 ) and stress ( 0.78 ) subscales . work and social adjustment scale ( wsas : 24 ) . the wsas is a 5-item measure asking participants to rate the degree of interference caused by their symptoms in work , home management , private leisure , social leisure , and family relationships . interference is rated over the past week on a 0 to 8 scale ( 0= not at all interfering to 8 = severe interference ) . the wsas has shown adequate internal consistency , ranging from 0.70 to 0.94 , and test - retest correlation ( 0.73 ) in a clinical sample ( 23 ) . wsas had a correlation with dass - d ( r=0.75 , p<0.01 ) and dass - a ( r=0.66 , p<0.01 ) and test retest reliability of wsas was statistically significant ( r=0.69 , p<0.01 ) . forty one participants ( in tow groups ) were enough to gain appropriate statistical power for testing hypotheses . people with inclusion and exclusion criteria were selected and assigned randomly to experimental and control groups . this study was carried out in akhavan hospital , tehran iran during may and june 2011 . the inclusion criteria included as anxiety and depressive symptoms based on the cut - off of 18 and higher in the depression subscale and score of 16 and higher in the anxiety subscale of the depression , anxiety , and stress scale ( dass-42 ; 20 ) . these cut - offs were determined based on the lovibond and lovibond s ( 15 ) method that used percentage points for determination of severity levels . according to this matter , the percentage points of 78 and higher formed low level of severity . the exclusion criteria was based on the axis i disorders , including anxiety disorders , depression , psychosis , psychosomatic and drug abuse , by using the anxiety disorders interview schedule for dsm - iv ( adis - iv ) . participants who obtained a score equal to or greater than 18 in depression subscale and 16 in subscale of anxiety evaluated based on the anxiety disorder interview schedule for dsm - iv in order to determine inclusion and exclusion criteria . then , we explained the study , its conditions , and moral status to them and got the informed consent , after that the study instruments were administrated and readministered after treatment sessions . the study administrated on the students population of universities across tehran city . among all prepared participants , only data of 33 students analyzed after the end of invention . 16 students assigned at control group ( cognitive group therapy ) , and 17 students in transdiagnostic group . the mean ( standard deviation ) age of the participants was 22.6 ( sd=3.1 ) . results showed that experimental group s age with mean ( standard deviation ) of 22.88 ( 1.62 ) and control group mean ( standard deviation ) of 23.75 ( 2.75 ) statistically not significant ( m= 0.87 ; sd= 0.77 ; t= 1.12 ; p < 0.27 ) . in addition , differences between genders in two group not statistically significant using chi square test ( x=0.24 & p < 0.62 ) . the participants filled out demographic and informed consent at intake . in addition , all of them completed the wsas and dass questionnaires . then , they assigned randomly to the experimental and control groups . they participated in the group cognitive therapy ( 16 ) and transdiagnostic group therapy ( 17 ) for 8-sessions per week ( a two - hour session ) . sessions content , procedures , and techniques were based on the published and known therapeutic instructions ( 16 , 17 ) . two absent sessions was permissible and three absent sessions was considered as drop - out . the anxiety disorders interview schedule for dsm - iv ( adis - iv ; ( 18 ) ) , is a semi - structured diagnostic interview designed to assess the presence , nature , and severity of dsm - iv anxiety , mood , and somatoform disorders , as well as previous mental health history . the interview also contains a brief screen for psychotic symptoms , and alcohol and substance abuse . all adis - iv interviewers , advanced doctoral students , were trained to rigorous standards for reliability with an expert adis - iv interviewer . this measure has demonstrated acceptableto excellent interrater reliability for the anxiety and mood disorders ( 19 ) . the depression , anxiety , and stress scale ( dass;(15 ) ) is a 42-item self - report measure in which participants rate the frequency and severity of experiencing negative emotions . the dass is comprised of three subscales , physical symptoms of anxiety ( dass - a ) , mental stress ( dass - s ) , and depression ( dass - d ) . each of 42 symptoms is presented as an item , and is rated on a 4-point frequency and severity scale . internal consistencies for all three factors were in the very good to excellent range ( dass - d 0.91 ; dass - a 0.84 ; dass - s 0.90 ) . the depression , anxiety and stress subscales have shown strong psychometric properties with a range of populations ( 15 , 21 ) . they were reported good internal validity for depression ( 0.77 ) , anxiety ( 0.79 ) and stress ( 0.78 ) subscales . work and social adjustment scale ( wsas : 24 ) . the wsas is a 5-item measure asking participants to rate the degree of interference caused by their symptoms in work , home management , private leisure , social leisure , and family relationships . interference is rated over the past week on a 0 to 8 scale ( 0= not at all interfering to 8 = severe interference ) . the wsas has shown adequate internal consistency , ranging from 0.70 to 0.94 , and test - retest correlation ( 0.73 ) in a clinical sample ( 23 ) . wsas had a correlation with dass - d ( r=0.75 , p<0.01 ) and dass - a ( r=0.66 , p<0.01 ) and test retest reliability of wsas was statistically significant ( r=0.69 , p<0.01 ) . an independent t test was used to examine the age difference between control and experimental groups . the results explained that there was not any significant difference in age ( m=0.87 , sd=0.77 , p=0.27 ) between experimental group ( m=22.88 , sd=1.62 ) and control group ( m=23.75 , sd=2.72 ) . mean and there was not a significant difference between variables in t - test comparing the means . thus , there was not any significant difference between two groups on the symptoms of anxiety , depression , and general performance in pre test . the results of dependent t test have been displayed in table 2 that shows transdiagnostic group therapy was significant in all variables . in fact , it was significant in depressive symptoms reduction ( t=13.09 ) , anxiety ( t=13.75 ) and stress ( t=6.48 ) at the level of 0.001 . moreover , it led to general performance improvement in the group that was measured by work and social adjustment scale ( t=6.93 , p>0.001 ) . the cognitive group therapy was considered as a control group and it caused a significant change in all variables . the results illustrated that the cognitive group therapy could reduce significantly symptoms of depression , anxiety , and stress . , the cognitive group therapy provided significant changes ( t=7.36 , p > 0.001 ) and improved general performance among group . the comparison of two groups results are shown in table 4 and explained that there was not any significant difference between transdiagnostic and cognitive therapy in non of the variables expect anxiety ( f=9.22 , p=0.005 ) . in other words , the transdiagnostic group therapy illustrated a significant difference in anxiety reduction not cognitive group therapy . there was not a significant difference between variables in t - test comparing the means . thus , there was not any significant difference between two groups on the symptoms of anxiety , depression , and general performance in pre test . the results of dependent t test have been displayed in table 2 that shows transdiagnostic group therapy was significant in all variables . in fact , it was significant in depressive symptoms reduction ( t=13.09 ) , anxiety ( t=13.75 ) and stress ( t=6.48 ) at the level of 0.001 . moreover , it led to general performance improvement in the group that was measured by work and social adjustment scale ( t=6.93 , p>0.001 ) . the cognitive group therapy was considered as a control group and it caused a significant change in all variables . results are showen in table 3 . the results illustrated that the cognitive group therapy could reduce significantly symptoms of depression , anxiety , and stress . these results are statistically significant respectively ( t=9.08 , t=8.04 , t=7.51 ; p>0.001 ) . in addition , the cognitive group therapy provided significant changes ( t=7.36 , p > 0.001 ) and improved general performance among group . the comparison of two groups results are shown in table 4 and explained that there was not any significant difference between transdiagnostic and cognitive therapy in non of the variables expect anxiety ( f=9.22 , p=0.005 ) . in other words , the transdiagnostic group therapy illustrated a significant difference in anxiety reduction not cognitive group therapy . the present study evaluates the effectiveness of transdiagnostic group therapy and compares it to standard cognitive group therapy in reduction of anxiety and depressive symptoms and improvement of general performance . the findings confirm study hypothesis based on the effectiveness of transdiagnostic group therapy in reduction of emotional components and improvement of general performance . in comparing post - test scores for two groups , a significant difference generally , we can conclude that transdiagnostic group therapy can reduce anxiety and depression same as cognitive therapy . however , transdiagnostic group therapy is superior to cognitive therapy in reduction of anxiety symptoms , because the transdiagnostic approach is a unified ( 8) and reduces the anxiety by techniques such as emotional and interoceptive exposure ( 25 ) . ( 12 ) in the primary study in order to construct and evaluate the primary protocol found that transdiagnostic treatment could be effective for a range of emotional disorders . boisseau and his colleagues reported the similar results on a case study ( 26 ) . indicative prevention based on cognitive approach could reduce effectively symptoms of depression and anxiety among students population ( 27 ) . generally , the transdiagnostic approach have benefits in the treatment and prevention of mental disorders including the dissemination and accessibility , high capacity in applying for a group , their application for most of emotional disorders and relapse prevention . clark and taylor ( 28 ) believed that there was no need to replace transdiagnostic cognitive behavioral therapy with disorder specific therapies . although , they declared that transdiagnostic therapies could be applied as a complimentary treatment for empirical supported treatments . in other words , transdiagnostic therapies can be used before specific therapies in order to train general skills and coping with problems . clark and taylor ( 28 ) explained three major problems for specific cognitive behavioral therapies :  ( a ) failure to demonstrate a significant additive advantage of cognitive ingredients over  purely  behavioral interventions , ( b ) difficulty in establishing cognitive mediation , and ( c ) neglect of common or shared features across disorders therapeutic programs based on transdiagnostic approach were effective , but it was necessary to investigate inclusion and exclusion criteria , severity of target disorders and multiple comorbidities in the therapy ( 29 ) . moreover , therapeutic protocols should have less complexity . for example , selective attention to treat is most likely to be experienced by individuals with anxiety disorders but its content can be different in a variety of anxiety disorders . the transdiagnostic therapies are process oriented and the main diagnosis is not important in the therapies . although , there are some limitations for this approach , more studies should be applied to answer the questions related to this novel approach ( 28 ) . there may be limitations with respect to the generality of the findings because of sample selection that was among college students . on the other hand , drop out in the sample had been occurred because of some reasons , in fact , 20% drop out took placed in the session s procedure . there were some reasons for dropping out such as : educational problems and transportation problems . applying both methods of interventions by the researcher caused individual biases that were other research limitations . recommending the future studies apply transdiagnostic interventions in the selective and universal prevention research . in addition , the study of this therapeutic model can be conducted in a variety of samples such as children , elderly and in different levels like school , family , and multi level . we believed that protective , mediator and moderator factors investigation could be done for emotional disorders . furthermore , a long - term follow up for outcomes of transdiagnostic group therapy is suggested . the study of transdiagnostic therapy mechanism and its effectiveness in the other disorders and problems is necessary for the procedure dismantling studies ( 12 ) . finally , it seems that transdiagnostic interventions need to more investigations to compare specific intervention and the other disorders with this approach . ethical issues ( including plagiarism , informed consent , misconduct , data fabrication and/or falsification , double publication and/or submission , redundancy , etc ) have been completely observed by the authors .