Introduction
Arthritis is a leading cause of disability in older people and is one of the major medical challenges due to the increase in life expectancy in developed and developing countries and the increase of the elderly [1]. Patients with knee osteoarthritis often complain of pain, muscle weakness, decreased range of motion, and reduced functional ability of the joint involved [2]. In the United States, the population growth of the elderly over the age of 65 was higher than the total population growth between 2000 and 2010 [3]. The prevalence of arthritis in Iran is 16.6% in urban areas and 20.5% in rural areas; the most affected joint in rural areas belongs to the knee joint [4]. Total knee replacement is one of the most common methods to reduce pain, improve joint function, increase physical activity, and improve quality of life (QoL) [5]. Surgeons can directly assess the disorder-related outcomes such as the knee range of motion by physical examinations; however, they need assessment tools based on patient reported outcome measures to assess the success of treatment after knee replacement [6]. 
Physical activity assessment tools designed specifically for a disease can better assess the results of therapeutic interventions [7]. Specific activity assessment tools include the University of California at Los Angeles Activity Scale (UCLA), activity rating scale (ARS), and tegner activity scale (TAC) [5]. In 1998, Zahiri et al. numerically compared the gait activity of patients with total knee replacement and measured their activity in three different modes using the UCLA and pedometers. In the first mode, each patient was assessed using a 10-level scoring system for the UCLA rating. The second and third modes were based on using a simple visual analog scale. They found that the UCLA activity rating (P=0.002) and visual analog scale rating of the investigator (P <0.001) had a strong correlation with the activities recoded by the pedometer. Thy concluded that both the UCLA activity rating and the investigator’s visual analog scale are valid for assessing patients’ routine activity in a clinical setting [1]. For Chinese and Italian versions of the UCLA in candidates for hip and knee replacement, the results showed excellent reproducibility and acceptable validity of the scale (8, 9). The main purpose of this study was to translate and localize the UCLA and evaluate the psychometric properties including reliability and validity of the Persian version of the UCLA.
Materials and Methods
Study design and participants
This study was approved by the ethics committee of Mashhad University of Medical Sciences (Code: IR.MUMS.REC.1398.283). First, the Persian version of the UCLA questionnaire was translated in three steps (standard forward translation, translation synthesis, and backward translation) according to International Quality of Life Assessment (IQOLA) protocol. Participants were 103 patients who were candidates for knee replacement based on the diagnosis of an orthopedic physician who were selected by simple sampling method from December 2009 to November 2020 in Mashhad, Iran. All participants signed an informed consent form to participate in the study. The Persian UCLA, the TAS, 36-item short form survey (SF-36), and the international physical activity questionnaire (IPAQ) were then completed by them. The Persian UCLA was re-completed by 66 participants in the test-retest phase at intervals of 3-7 days, with no change in physical condition approved by the patient and the physician. 
Tools 
The UCLA Activity Scale, developed in 1998, is a simple tool with rating range of 1-10, where a higher score indicates better lower limb activity. Score 1 indicates the complete dependence on others and being unable to leave home, while score 10 shows the ability to participate in active and impact sports such as jogging, tennis, skiing, acrobatics [11].  The TAS is a single-item scale that rates the work and sports activities. It is numerically scaled from 0 to 10; each score indicates the ability to perform a series of specific activities. The score 10 shows the ability to participate in competitive sports including football and rugby at the national level [12]. This questionnaire has been translated into Persian and validated [13]. 
The SF-36 is a self-reported questionnaire with 36 items measuring a person’s general health. It includes 8 subscales: Physical functioning, role physical, bodily pain, general health, vitality, social functioning, mental health, and role emotional. These subscales yield two summary measures, physical health (physical functioning, role physical, bodily pain, and general health) and mental health (vitality, social functioning, and role emotional) [14]. The Persian version of the SF-36 has acceptable psychometric properties [15]. 
The IPAQ is a general questionnaire designed to assess a person’s health-related physical activity over the past week. It has 27 items and four parts: Job-related physical activity with 7 items, transportation physical activity with 6 items, housework with 6 items and, leisure-time physical activity/sports/recreation with 6 items. In addition, there is one part with two items to assess the time spent sitting while at work, at home or during leisure time in the last 7 days. Based on the answers to the questions, the level of physical activity is divided into low, moderate or high. This questionnaire has been translated into Persian and validated [16]. 
Evaluation of psychometric properties 
Relative and absolute reproducibility of the Persian UCLA were evaluated by obtaining test-retest reliability, intraclass correlation coefficient (ICC) calculation, and standard error of measurement (SEM) calculation, which is an index of absolute reproducibility. To obtain test-retest reliability, the data were recorded for the second time at intervals of 3-7 days after the first data were recorded. The ICC and UCLA scores were used in two measures for a number of samples selected from the target population. An ICC ≥0.70 shows acceptable test-retest reliability. The SEM was obtained using ANOVA. SEM is used to calculate the smallest detectable change (SDC) in an individual’s score. The SDC can be considered as a clinical measure of change in activity level. The SDC is defined at the 95% confidence interval of SEM (95% [±1.96] SEM) [12]. 
The convergent validity was determined by examining the correlation of the Persian UCLA with the TAS, SF-36, and IPAQ. Roos et al. reported that the correlation coefficients of convergent validity range from 0.20 to 0.60 and rarely above 0.70 [17]. Therefore, a correlation coefficient <0.20 shows weak correlation, 0.20-0.60 indicates moderate correlation, and >0.60 shows strong correlation. The ceiling and floor effects were also evaluated. These effects are considered present if more than 15% of patients archived the highest and lowest scores [13, 18]. Therefore, in this study, the response rate to the physical activity level 1 (lowest activity level) was considered as the floor effect and the response rate to the physical activity level 10 (highest activity level) was considered as the ceiling effect.
The evaluation of psychometric properties of the Persian UCLA was done in SPSS software v. 19 at a significance level of P<0.05. Kolmogorov-Smirnov test was used to evaluate the normality of data distribution. 
Results
During the translation process, no specific changes were made in the items of the UCLA and no problem or ambiguity was reported by the respondents based on a pilot study. The type of exercises mentioned in the main version of UCLA was not changed either. None of the participants complained about the difficulty understanding the items. Demographic and clinical characteristics of patients who completed the questionnaire are shown in Table 1.


The data of UCLA had a normal distribution (P=0.08), while TAS (P=0.04), SF-36’s physical health summary measure (P=0.04) mental health summary measure (P=0.01), and IPAQ (P=0.001) had abnormal data distribution.
The mean and standard deviation of the Persian UCLA score were obtained 2.98±1.37 in the first stage and 2.1±89.32 at the intervals of 3-7 days in the second stage. Psychometric tests results showed acceptable test-retest reliability of the Persian UCLA (ICC=0.96; 95% CI: 0.93-0.97). Considering the SDC score as 0.50, if the UCLA score is above or less than 0.50, an improvement or decline in the physical activity level clinically happen at 95% confidence interval.
All study hypotheses were confirmed based on the results of Spearman correlation test. There was a strong correlation between the scores of Persian UCLA and TAS (rs=0.71, P<0.001), a moderate correlation between the scores of Persian UCLA and IPAQ (rs=0.58, P<0.001) and between the scores of Persian UCLA and physical health summary measure of SF-36 (rs=0.59, P<0.001), while there was a weaker moderate correlation between the scores of Persian UCLA and mental health summary measure of SF-36 (rs=0.39, P<0.001). The response rate to the lowest activity level (score 1) was 4.9%, while the response rate to the highest activity level (score 10) was zero. Therefore, the Persian UCLA had no ceiling or floor effects. 
Discussion 
Examining the psychometric properties of the Persian UCLA questionnaire showed that it had acceptable test-retest reliability and convergent validity with no ceiling and floor effects. Reproducibility is considered as an important factor to choose a suitable measurement tool. The Persian UCLA questionnaire had great reproducibility of ICC=0.96, which is consistent with the results of Chinese version (ICC=0.94) and Italian version (ICC=0.99) (8, 9). The SDC score was less than the minimum score of the questionnaire (1 point). Considering the SDC equal to 0.50 at 95% confidence interval, patients' physical activity level got better or worse when the change in the 10-point range of the UCLA questionnaire was less than or higher than 0.50. The SDC equal to 0.50 in the Persian version is comparable to the SDC equal to 0.83 in the Chinese version. However, further studies are recommended to evaluate the response rate in the Persian UCLA to be able to speak more conclusively about the change in the activity level after various therapeutic interventions. 
The convergent validity of the Persian UCLA was assessed by calculating the Spearman correlation coefficient (r) with the Persian versions of TAS, IPAQ and SF-36 questionnaires. The results showed the strong correlation of Persian UCLA score with the TAS score, a moderate correlation with IPAQ score and the physical health summary measure of the SF-36, and a weak correlation with the mental health summary measure of SF-36. Based on the strong correlation between the UCLA and TAS, they evaluate the physical activity level similarly. The Persian UCLA had the highest correlation between the TAS (rs=0.71) and lowest correlation with the SF-36’s mental health summary component (rs=0.39). Since the most of the problems of patients with knee osteoarthritis are related to the ability to perform routine physical activities [19], the UCLA activity scale is able to detect important problems of these patients and assess their physical activity level. The results of evaluating the validity of the Persian UCLA are consistent with the results of the Chinese version in patients who were candidates for knee prosthesis. Pearson correlation coefficient of the Chinese UCLA with the TAS was 0.63 (P<0.001) which shows a strong correlation. Pearson correlation coefficient of the Chinese UCLA with the SF-36 subscales of physical functioning, general health, bodily pain (subscales of physical health summary measure), and social functioning (subscale of mental health summary measure) was about 0.48-0.68 (P<0.001), which indicates a moderate to strong correlation; with the subscales of role physical (subscale of physical health summary measure) and vitality (subscale of mental health summary measure), the correlation coefficient was about 0.28-0.32 (P<0.001) which indicates a moderate correlation. Two SF-36 subscales of role emotional (subscale of mental health component) (r=0.19, P=0.54) and mental health (subscale of mental health summary measure) had no statistically significant correlation (r=0.14, P=0.16) [8]. For the Italian UCLA in candidates for hip prosthesis, results indicated the strong correlation of this version with the total score of the Western Ontario and McMaster Universities Arthritis Index (r=0.67, P<0.001), Harris hip score (r=0.68, P<0.001), the SF-12’s physical health summary component (r=0.67, P<0.001) and Oxford hip score (r=0.67, P<0.001), and a moderate correlation with the SF-12’s mental health summary component (r=0.37, P<0.001) [9]. 
The assessment tools should have the ceiling and floor effects less than 15% (20). In this study, the ceiling effect was zero and the floor effect was 4.9% for the Persian UCLA questionnaire. Given that most patients with knee osteoarthritis report their problems regarding inability to perform routine physical activities (such as housework, walking, etc.), the range of answers in the UCLA was able to show the common problems of these patients correctly. Based on the evaluation of orthopedic and rehabilitation specialists, the ceiling and floor effects of the Chinese version were also acceptable [8]. The information for all 10 activity levels of the questionnaire was sufficient to assess the functioning of candidates for knee prosthesis. In the Chinese version of UCLA, the ceiling effect was 1% and the floor effect was 5.5% [8]. 
The present study had some limitations, including the study samples, which may not be a complete representation of Iranian population. There are cultural and linguistic differences between different Iranian ethnicities. Moreover, there was no study on responsiveness property of the Persian UCL, so we recommend future studies conduct a study to investigate this important measurement property.
Conclusion 
The Persian UCLA has acceptable psychometric properties such as reproducibility, convergent validity and content to determine the level of physical activity in candidates for knee replacement. 

Ethical Considerations
Compliance with ethical guidelines
Ethical principles were fully observed in this article. Participants were allowed to leave the study at any time and were informed about the study process and that their information would be kept confidential. This study obtained its ethical approval from the ethics committee of Mashhad University of Medical Sciences (Code: IR.MUMS.REC.1398.283).

Funding
This study is taken from Hadi Khoshrou's master's thesis in the Department of Physiotherapy, Faculty of Paramedical Sciences, Mashhad University of Medical Sciences with number 981038. Mashhad University of Medical Sciences has financially supported this study.

Authors' contributions
Conceptualization: Neda Mostafaei, Hossein Gardhan, Hadi Khoshro and Seyed Javad Raisi; Supervision and management of the project: Neda Mostafaei and Hossein Gardhan; Methodology: Neda Mostafaei and Hossein Gardhan; Data collection: Hadi Khoshro and Seyed Javad Raisi; Writing the draft: Hadi Khoshro; Data analysis: Neda Mostafaei; Editing and finalization of the article: all authors.

Conflict of interest
The authors declare no conflict of interest.

Acknowledgments
The authors would like to thank Mashhad University of Medical Sciences for the financial support.


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