Introduction
Social isolation of the elderly is one of the major global concerns. Social isolation, which is characterized by the lack or limitation of social interactions between people [1], is one of the most important risk factors for chronic diseases, but there is low knowledge about it [2, 3, 4]. Social isolation consists of two objective (social disconnectedness) and subjective (perceived isolation) dimensions [2, 5]. The objective dimension includes tangible aspects such as physical separation and lack of interaction with others [6] while the subjective dimension includes the feeling of loneliness and the perception of lack of social support [7]. The objective and subjective dimensions of social isolation are distinct from each other and the experience of one of them does not necessarily mean the experience of the other [8]. Despite the importance of examining the objective and subjective dimensions at the same time, most of the existing tools only examine one of these dimensions. The social disconnectedness/perceived isolation scale is among the few tools for simultaneously investigating the objective and subjective dimensions of social isolation among the elderly [5, 7]. The social disconnectedness scale has a two-factor structure, including the restricted social network dimension and the social inactivity dimension. The perceived isolation scale also comprises two dimensions: lack of support and loneliness. It was developed by Cornwell and White [5, 7]. This study aims to evaluate the psychometric properties of the Persian versions of the social disconnectedness and perceived isolation scales for Iranian older adults.
Methods
The steps of translation and back-translation were carried out according to the standard protocol of the World Health Organization [9] with permission from the designers of the scales. Validation of the scales was done in a sample of 390 older adults aged 60 years or more in Tabriz, Iran who were selected by a cluster sampling method with probability proportional to size. Face validity was determined after face-to-face interviews with 15 older adults. The content validity index (CVI) and the content validity ratio (CVR) were examined based on the opinions of a panel of experts. The minimum acceptable value of CVR based on the number of experts and the Lawshe table is ≥0.49 [10] and the minimum acceptable value of CVI is ≤ 0.80 [11]. Due to cultural differences, the “partner” domain was removed from the list of restricted social network dimension. Also, participation in religious ceremonies and congregational prayers were added as examples of group activities. In addition, participating in activities such as helping to feed, educate and treat the poor and needy people, helping with mosque affairs and holding religious ceremonies were added as examples of voluntary activities. Exploratory factor analysis (EFA) was used to investigate the factor structure. The structure of the studied scales was checked by confirmatory factor analysis (CFA). To determine reliability, two methods of calculating Cronbach’s alpha coefficient and intraclass correlation coefficient (ICC) were used. Data analysis was done in SPSS version 23 and AMOS version 18 software.
Results
Of 390 participants, 212(54.4%) were men and 178(45.6%) were women. Their mean age was 68.9±7.7 years. For the social disconnectedness scale, CVR=0.98 and CVI=0.91 and for the perceived isolation scale CVR=0.91 and CVI=0.96. The sampling adequacy test Kaiser-Meyer-Olkin (KMO) for the two scales of social disconnectedness (0.701) and perceived isolation (0.750) showed the adequacy of sampling and the feasibility of factor analysis.
EFA with Varimax rotation showed that 8 items of the Persian version of the social disconnectedness scale supported a three-factor structure. The social inactivity dimension was confirmed in the Persian version, while the restricted social network dimension was divided into two factors of family-oriented and community-oriented. The amount of variance explained by the 3-factor structure of the Persian version of the social disconnectedness scale was 58.7%. CFA and structural equation modeling confirmed the three-factor structure of the Persian version of the social disconnectedness scale (RMSEA=0.050, GFI=0.951, CFI=0.950, and TLI=0.955).
EFA with varimax rotation showed that 9 items of the Persian version of the Perceived Isolation Scale supported a four-factor structure. The lack of support dimension was divided into three sub-factors of lack of support from family members (2 items), friends (2 items), and spouse (2 items). The amount of variance explained by the 4-factor structure of the Persian version of the Perceived Isolation Scale was 81.1%. The items and factors of the original version and the Persian version of the two scales are shown in Table 1.


CFA and structural equation modeling confirmed the 4-factor structure of the Persian version of perceived isolation scale (RMSEA=0.045, GFI=0.955, CFI=0.955, and TLI=0.950).
Cronbach’s alpha was 0.64 the social disconnectedness scale and 0.76 for the perceived isolation scale. Also, the ICC ranged 0.77-0.97 for the social disconnectedness scale and 0.73-0.92 for the perceived isolation scale.
Discussion
Understanding the characteristics of the social networks of the elderly provides valuable information for planning and designing preventive interventions for the social isolation of the elderly [12]. The main purpose of the present study was to investigate the psychometric properties and factor structure of the Persian version of the social disconnectedness/perceived isolation scale for Iranian elderly. The EFA results showed the emergence of different factors in the Persian version of the disconnectedness/perceived isolation scale. The difference due to cultural and ethnic differences and other sociological components, including social norms. The importance of the types of relationships in the personal social network is different in different cultures [13]. Although the Persian version of the social disconnectedness/perceived isolation scale has a different factor structure from that of the main version, it has good validity and reliability for use in Iranian older adults for measurement and interventions in the field of social isolation.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the ethics committee of Tabriz University of Medical Sciences (Code: IR.TBZMED.REC.1398.768)

Funding
This study was extracted from a PhD thesis. It was funded by Tabriz University of Medical Sciences.

Authors' contributions
Conceptualization, data collection and analysis: Akbar Azizi Zeinalhajlou; Conceptualization,, design, data analysis: Abdol Rasoul Safaeian;  supervision, initial draft preparation: Haidar Nadrian; editing & review: Mina Hashemiparast; initial draft preparation: Mohammad Bagher Alizaddeh Aghdam; Conceptualization and project administration: Hosein Matlabi; final approval: All authors.

Conflicts of interest
The authors declare no conflict of interest.

Acknowledgements
The authors would like to thank Tabriz University of Medical Sciences for their support.

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