Background: Frailty syndrome involves a complex combination of the natural process of getting old with different medical problems. Different indexes have been designed for each physical, mental, and social dimensions of frailty. Fried’s five-item index of frailty syndrome checklist is one of the most applicable scales to screen frailty. This study aimed to determine a psychometric index of frailty and the cut-off points for the Iranian elderly population.
Methods: In a cross-sectional and psychpmetric study, 249 frail elderly people were selected among members of two Iranian Army Retirees Clubs in 2019. This was a cross-sectional-psychometric study which aimed at 
determining the psychometric index and cut-off points of a brief checklist of 5-item FSC among Iranian adults older than 60 years old and comparing this to prior results in different countries.
Results: The data were analyzed by ANOVA, multi-variable regression, confirmatory, and exploratory factor analysis, and ROC analysis via SPSS 25 and AMOS 24. The validity of the study findings was determined by internal validity, high correlation of 5 questions, confirmatory and exploratory factor analysis of 3 subdomains with a clarity value of 0.87, and high goodness of fit index (GFI).
Conclusion: The determined cut-off points were compatible with those of Fried’s prior study. The designed tools used in this study evaluated frailty syndrome of the Iranian elderly in elderly rehabilitation studies with high confidence. The application of the tool would provide caregivers and policymakers with additional information as to caring for this population.
Introduction
The world population has become older due to the decreasing mortality rate, increasing life expectancy, and enhanced healthcare technologies.⁽¹⁾ Worldwide, the elderly population is expected to increase from 9% to 16% during 35 years from 1995 to 2030. Regionally, the elderly population is expected to increase in Asia and Iran from 9.3% to 18.6% and from 5.17 to 6.5 % over the same period, respectively.⁽²⁾ Increased chronic diseases and multi-morbidity in the elderly and the associated increased prevalence of inabilities are the main concern in the growth of the elderly population . Senescence syndromes are groups of prevalent characteristics among the elderly and, as such, are not considered a disease. These syndromes are a group of prevalent characteristics among the elderly, which are not considered a disease. Frailty syndrome involves a complex combination of the natural processes of getting old with different medical problems,⁽³⁾such as weakness, dullness, decreased energy, decreased physical activity, and unintentional weight loss (in more intense cases).⁽³⁾Frailty syndrome consists of physiological disorders in six different systems (hematic, inflammatory, hormonal, obesity, neuromuscular, and nutritional).⁽⁴⁾ The brain, endocrine, musculoskeletal, and immune systems are mostly associated with frailty syndrome, which have been studied considerably.⁽⁴⁾ The prevalence of frailty due to its wide definition and variety of measurement tools is estimated 19.6% in Latin America and the Caribbean ⁽⁵⁾, from 3.9 per cent in China to 26% and 51.4% in India and Cuba, respectively ⁽⁶⁾, 35.7% in Brazil ⁽⁷⁾,  10% in Japan ⁽⁸⁾, and in European countries from 7.7 per cent of the Swedish elderly to 15.6% Portuguese older adults ⁽⁹⁾. There are no national frailty data in the elderly population of Iran, bBut it can be assumed to be similar to developing countries like India and Brazil. Most of the tools developed to evaluate frailty have a frailty pre-diagnosis, enabling the authorities to identify people at high risk of frailty.^{(10, 11)}
Frailty can be examined in both clinical and social contexts. The clinical view argues that frailty increases the risks of side effects, such as fall, hospitalization, inability, and death.⁽¹²⁾ The social view identifies the groups in need of  additional medical care services and at high risk of dependency.⁽¹²⁾ Policymakers and providers of health services have realized that frailty could significantly affect people, caregivers, healthcare systems, and society^{.(11, 12)} Furthermore,  concerns have been raised regarding prevention and health management plans due to the effect of frailty on the healthcare of patients^.(13) If frailty can be diagnosed, prevented, and treated by identifying its different reasons and factors, this can lead to the prevention or at least  delay in the onset of frailty syndrome. As some recent studies have suggested, frailty sequences could be reversed by implementing specific practical plans and nutritional supplements ^{(3, 14, 15)}. Therefore, identification of consequences relevant to frailty is highly vital, indicating the need for a tool to predict frailty challenges in Iran. These challenges can be screened, and definite cut-off points can be determined for Iranian frail patients. These actions help the healthcare policymakers in the country to systemize and optimize their decisions, just as many developed countries have done in recent years^.(16) Fried’s five-item index of frailty syndrome checklist (5-Item FSC) is one of the most applicable scales to screen frailty.⁽¹⁶⁾
Psychometric properties and cut-off points of FSC differ from one country to another regarding their cultural, social, nutritional, and even phenotypical differences ⁽¹⁷⁾ compared to other indices. Therefore, the present study aimed to determine the validity, reliability, and cut-off points of 5-item FSC for Iranian elderly.