Introduction
Relationship obsessive-compulsive disorder (ROCD) is a crucial subtype of obsessive-compulsive disorder (OCD) [9]. It is characterized by obsessions and unwanted thoughts about intimate relations and has two main dimensions: partner-focused and relationship-centered. The relationship-centered ROCD has symptoms such as doubts about the partner’s feelings toward oneself, one’s feelings toward their partner, and the “rightness” of the relationship [15]. The partner-focused ROCD involves disturbing thoughts and doubts about flaws perceived in the partner across areas such as appearance, morality, intelligence [13]. A common type of partner-focused ROCD is Obsessive Distrust, which can be identified by obsessive doubts and preoccupations with the untrustworthiness or unreliability perceived in the partner, and compulsive behaviors related to jealousy such as constantly checking the partners’ things and behaviors [17]. 
Based on the literature, there is a connection between partner-focused ROCD  and many personal and marital issues, such as poor emotional status, mood disorders, and less satisfaction from sexual activity [19]. The diagnosis of ROCD may be challenging. The individuals with this disorder may not seek the advice of a specialist [20]. it is necessary to maintain a valid and reliable instrument to measure ROCD. One of these tools in the obsessive distrust inventory (ODIS) designed by Doron, Brands, and Stern in 2020. It is an 8-item tool with a 5-point Likert scale [4]. In this study, we aimed to assess the psychometric properties of the Persian version of ODIS.

Methods
Participants were 365 married students over 18 years old from Shahid Beheshti University of Medical Sciences in 2021-2022, who were selected by a convenience sampling method. After the translation by the back-translation method, the questionnaires including ODIS, Obsessive Compulsive Inventory-Revised (OCIR), Depression Anxiety Stress Scale-21 (DASS-21), and Partner-Related Obsessive–Compulsive Symptoms Inventory (PROCSI) were distributed among the participants. The collected data were analyzed in SPSS software, version 24 and Amos version 24. The composite reliability of Persian ODIS was assessed, and its internal consistency was determined using Cronbach’s alpha and omega coefficients. The construct validity was assessed by using confirmatory factor analysis (CFA). To measure the convergent validity, the Average Variance Extracted (AVE) index was calculated. The AVE value is acceptable if it is more than 0.5.

Results
The mean age of the participants was 28.67 ± 8.75 years. Of 365 participants, 277 (79.9%) were women and 88 (19.3%) were men. Also. 64 (14%) had a diploma, 30 (6.6%) had an associate degree, 198 (43.3%) had a bachelor’s degree, 109 (23.9%) had a master’s degree, 25 (5.5%) had PhD, and 31(6.8%) had a professional doctorate.
Bartlett’s test result (3185.26) was significant (P<0.01), indicating that the scale was appropriate for factor analysis. Moreover, the KMO index was obtained at 0.94, which was more than the acceptable value (0.7). The results of CFA on the single-factor structure of the Persian ODIS are shown in Table 1. Based on the results, the single-factor structure had a good fit.



The composite reliability value, Cronbach’s alpha coefficient value, and omega coefficient value were all reported as 0.94, which indicates good composite reliability and internal consistency of Persian ODIS. The AVE value was estimated at 0.69. Also, the correlation of the score of the ODIS with the scores of DASS-21, PROCSI, and OCIR was evaluated to determine its convergent validity. The results indicate a significant positive correlation among them (P<0.01), indicating the acceptable convergent validity of the Persian ODIS (Table 2).



Conclusion
Consistent with Brandes et al.’s study [17], the Persian ODIS had a single-factor structure. Cronbach’s alpha for the overall scale was reported as 0.94, which indicates good internal consistency of the Persian ODIS. Its score had a significant positive correlation with the scores of DASS-21, OCIR, and PROCSI, which indicates its good convergent validity. Therefore, the Persian ODIS has acceptable validity and reliability for measuring the ROCD in Iranian population. 

Ethical Considerations

Compliance with ethical guidelines
All ethical principles, such as obtaining informed consent from the participants and the confidentiality of their personal information, were considered in this study. This study was approved by the Ethics Committee of Shahid Beheshti University of Medical Sciences (Code: IR.SBMU.RETECH.REC.1400.1131).

Funding
This study was funded by the Student Research Committee of Shahid Beheshti University of Medical Sciences.

Authors contributions
Conceptualization: Amir Sam Kianimoghadam, Farnaz Doostadri, Mahyar Arzpeyma; Investigation: Mahyar Arzpeyma, Farnaz Doostdari; Editing & review: Farnaz Doostdari, Zahra Amanollahi; Supervision: Amir Sam Kianimoghadam.

Conflicts of interest
The author declared no conflict of interest.

Acknowledgments
The author would like to thank all the participants for their cooperation in this study.




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