Introduction
Recognizing the role of accurate information in decision-making, especially financial and cost information, we decided to design and apply a costing system for calculating the cost of services [2]. Costing and analyzing service costs can help hospital administrators, organization leaders, and policymakers scrutinize their units and institutions to meet people’s needs under their supervision and to what extent [3]. The importance of understanding cost structure has prompted organizations to turn away from the traditional costing approach (leading to the production of non-transparent information) toward activity-based costing or its new version, i.e. time-driven activity-based costing (TDABC) [4]. 
Rehabilitation services constitute a critical part of healthcare services, serving different sections of society. These services restore people’s functional ability and return them to society to fulfill their individual and societal functions. Pricing these services is one of the most important issues influencing access to rehabilitation services and their cost-effectiveness within the community. However, the crux of the issue lies in the meticulous determination of the price for such services. On the other hand, despite the critical nature of rehabilitation services, many remain outside of insurance coverage, and those in need of these services face more restrictions, further increasing the costs of disability and incapacitation in society. One of the vital prerequisites for health services to be covered is to accurately determine the actual cost of these services. Therefore, calculating the cost of rehabilitation services and enriching the related theoretical and empirical literature can represent a step towards providing greater financial transparency in this field and encouraging insurance companies to participate more in this sector.
Cost calculation methods have evolved in other countries in recent years, with the TDABC approach drawing much attention. Such studies conducted by Dimireh et al. on ambulatory emergency services [8], Tibor et al. on small bowel imaging services [9], Chen et al. on knee replacement surgery [10], Bodar et al. on laparoscopic pyeloplasty for children [11], and Parikh et al. on telemedicine in the COVID-19 period [12] have all employed TDABC for calculating the total cost.
Given the significant role of human resources costs in providing rehabilitation services, using traditional costing methods cannot result in accurate costing of these services. This study tries to calculate the cost of common services at the Nezam-Mafi Rehabilitation Center, Tehran City, Iran, based on the standard definition of services outlined in the book Relative Value Units of Services. For this purpose, the current study has calculated the cost of rehabilitation services with a new approach that considers the exact share of personnel costs (as the most important part of health costs). 

Materials and Methods
This descriptive study employed a cross-sectional and retrospective approach with regard to the use of performance-related data. Considering the significant role of calculating the cost for units providing rehabilitation services, this study was conducted to calculate the cost of outpatient rehabilitation services. Specifically, we examined speech therapy, occupational therapy, physiotherapy, and audiology services using the TDABC method at the Nezam-Mafi Rehabilitation Center. Regarding the variety of rehabilitation services, this study examined occupational therapy services (with national codes 901655 and 901630 in the book Relative Value Units of Services, third Edition), speech therapy (with national codes 900425 and 900420 in the book Relative Value Units of Services, third edition), physiotherapy (with national codes 901625 and 901645 in the book Relative Value Units of Services, third edition), and Audiology Services (with national codes 900475, 900485 and 900490 in the book Relative Value Units of Services, third edition).
Considering the outbreak of the COVID-19 epidemic since 2020 and the sharp decrease in referrals to rehabilitation centers, including Nezam-Mafi Rehabilitation Center, we chose the year 1398 in the Iranian calendar [AH], which spans from March 20, 2019, to March 20, 2020, as the study year. So, all of the financial and functional information in this year was included in the analysis. Nezam-Mafi Rehabilitation Center is a medical center affiliated with the University of Social Welfare and Rehabilitation Sciences, which has been operating since 2015 to provide rehabilitation services.
To determine the time equations related to different rehabilitation services, we timed the activities for 5 to 7 patients in each code/service, and its average was included in the calculations. The information related to the time of receiving the services of the patients was passive observation and without interaction with the patient. 
A workflow diagram was designed for each code service’s activities in the first step. Then, the different resources used by each activity were identified, and the cost for each activity was determined. The total cost amount was obtained for each cost group based on identifying cost groups and extracting related costs and their summation. The overhead costs were distributed to the departments by dividing the total cost by the cost driver and multiplying the resulting figure by the number of patients referred to each department. In distributing costs to cost centers, we carefully considered the activities of each center and selected the appropriate cost driver. The number of patients has been considered the driver of other overhead costs. The cost driver for human resources is their working minutes, which were measured by a timer. The driver of the cost of machines is their lifetime (in minutes), and the driver of the cost of repairs and maintenance of office equipment is the number of patients. For overhead and facility costs, meterage was considered as a cost driver. 

Results 
Table 1 presents the cost sources for the departments directly engaged with the patients.


The cost of renting the center, which is paid in the form of endowment rent, was the highest cost of the center in the year 1398 (Iranian calendar). Consumables, contract services, depreciation, and maintenance of assets were significant cost items in 1398 AH (Anno Hegirae [in the year of the Hijra]). Other cost items of the Nezam-Mafi Rehabilitation Center are classified and reported under 14 basic items. The lowest expenses recorded in 1398 AH were related to educational and research and mission expenses. 
Considering the costs mentioned above and their sharing in different departments based on the activity performed on them, we computed the cost of each service delivery unit in the various rehabilitation departments of Nezam-Mafi Rehabilitation Center in 1398 AH. According to the allotment of overhead costs, which encompassed two distinct categories—service overhead costs and meterage overhead costs—our approach factored in the number of referrals and the department floor area. Regarding the importance of personnel costs in calculating the cost of services, the TDABC method has focused on determining the time required to provide the service. To address this issue, we calculated the payment per minute of the staff presence in 1398 AH by considering the annual payment to the labor force of different departments and their presence in the service delivery departments. Notably, the highest human resources cost was related to the specialists working in the physiotherapy department, with an approximate payment of 7.456 Iranian Rials per minute of their presence in 1398 AH. Mental occupational therapists are in the next position, with a payment equal to 5.346 Iranian Rials. The total cost of staff at the Nezam-Mafi Rehabilitation Center is estimated at 3.904 Iranian Rials. This number, representing the third highest payment for human resources in this center in terms of amount, shows that the cost per minute of administrative personnel was higher than that of specialized labor in this center. 
After determining the source of costs, identifying the cost drivers, and calculating the unit price of different production sources, we proceeded to determine the service delivery drivers and the total cost of rehabilitation services in the Nezam-Mafi Rehabilitation Center. According to the information reported in Table 2, the specialized personnel and overhead costs constitute the main portion of the total cost of physiotherapy services.


In the occupational therapy department, the specialized personnel and building costs, and in the speech therapy department, office and personnel costs had the highest part in their services. The main part of the total cost related to audiology service codes was also associated with the cost of the office and overhead. Human resources had the highest cost share for code 901645 of physiotherapy. The expenses related to the equipment also comprised the highest share in providing physiotherapy service with the code 601625. Physiotherapy services with code 901625 and audiology with code 900490 also featured the highest cost components in their provision, particularly related to consumables, followed by overhead costs. 
The last step in calculating the total cost of rehabilitation services involves consolidating costs from different departments and accounting for the drivers necessary to provide the service. Table 3 reports the costs of each unit of the resources required to provide a service unit.


It can be seen that the cost of providing occupational therapy services at Nezam-Mafi Rehabilitation Center was the highest, and the physiotherapy service with the code 901625 was the cheapest in this center. 
After calculating the cost of each service, determining the service tariff becomes pivotal in ascertaining whether a service incurs profit or loss. According to the annual rate of public sector tariffs issued by the government, comparing the cost of all selected rehabilitation services in the Nezam-Mafi Rehabilitation Center with the official tariffs of these services in government centers shows that except for speech therapy service code 900420, the cost of providing other services was higher than their approved tariffs. The only service of Nezam-Mafi Rehabilitation Center whose provision costs less than the approved tariff was the 900420 service; the cost was about 70000 Iranian Rials less than the approved tariff. 

Discussion
The cost structure in the Nezam-Mafi Rehabilitation Center showed that the financial costs of rent, consumable materials and supplies, and contracted services had the highest share in the costs of providing rehabilitation services. The costing literature in rehabilitation services lacks applied case studies based on the TDABC approach [13]. It makes the cost of rehabilitation services unclear to providers, social insurance, and regulatory bodies. Understanding the cost structure and cost of services can help organizations provide high-quality goods and services in a competitive environment. Exploring this issue has been repeatedly emphasized in providing healthcare service providers [14, 15]. Following the purpose of the study, it was observed that the cost of providing most rehabilitation services in the Nezam-Mafi Rehabilitation Center is higher than the government tariffs for these services. Although Nezam Mafi Rehabilitation Center is a government service provider institution whose losses are compensated by the government budget, other rehabilitation centers likely run similarly [16, 17]. 
According to our research, the cost of the services (except a speech therapy service code) was higher than the approved tariffs for the services mentioned above. These results are consistent with the study on the cost of rehabilitation services in Asma Center [4]. Studies in other countries have also shown that service costs can be higher than its tariffs [8, 18, 19]. Nevertheless, studies with different results are also found in the literature [10, 20, 21]. Of course, the discrepancies were related to non-Iranian studies, and most studies conducted in Iran have indicated the high cost of health services and tariffs on the public and governmental sectors.
According to this research results and compared with the results of other studies, it can be concluded that various technical, organizational, and economic factors of a complex service influence the cost of providing it. Therefore, examining the cost structure of delivering services in treatment and rehabilitation centers can help to identify cost factors and optimal management of resources. Analyzing the cost structure for selected rehabilitation services in the Nezam-Mafi Rehabilitation Center showed that the share of different costs in these services was different depending on the type of service. Personnel costs allocate the highest share in physiotherapy services, as emphasized in many previous studies [4, 17, 20, 22]. 
The position of personnel costs in the cost of services and the need to manage these costs has made researchers more concerned about this part. Some researchers have emphasized the inevitability of these costs and highlighted the optimal use of personnel along with increased physical capital in proportion to the personnel [23]. Some others advocate for the development of the latest technical and accounting methods for gaining more accurate identification of costs caused by the compensation of human services. This study has been designed and implemented for this reason. Studies using the TDABC have estimated the share of human resources costs higher than those using other methods. For example, the study conducted by Jamie and Rezaie Yamin [24] underscores that about 73% of the expenses related to providing healthcare services in Isfahan Social Security Hospital were related to personnel expenses. 
A substantial portion of the cost of occupational therapy, speech therapy, and audiology services was related to the “office and building rental cost.” Therefore, avoiding rental costs (through reallocation of resources, such as merging with other rehabilitation institutions) can be vital in reducing the cost of services. In healthcare centers that provide services without property ownership, the share of building costs in the total costs is significant. Shaarbafchi zade et al. [25], in their study of the cost of hospital radiology and computerized tomography (CT) scan services, reported that the share of building costs was about 36.6% of the total costs. Of course, in the studies conducted in this field, the building costs have been ignored because most centers in which the cost is calculated are governmental (apart from considering the depreciation of the building in some studies). Considering the sharp increase in building costs in recent years in Iran, providing rehabilitation services in shared environments by avoiding geographical dispersion can help reduce the costs of service providers and bring profitability to the mentioned centers.
One significant component of the total cost contributing to the provision of rehabilitation services in the Nezam Mafi Rehabilitation Center was “overhead costs.” One of the major reasons for the high overhead costs is attributed to suboptimal service capacity utilization. This issue emphasizes the importance of production scale in a rehabilitation center. Considering this issue, it is expected that the increase in the number of patients in the  Nezam Mafi Rehabilitation Center will reduce the cost of each service unit and make its activities profitable. This finding has been emphasized in the study by Mohammadpour and others [4] in the rehabilitation center of Asma and Bahador et al. [26]. For other health and treatment services, the discussion of overhead costs has been considered considerably [27].
Conclusion
Considering that most rehabilitation services lack coverage by Iran’s social insurance and the current tariffs are not affordable for families in need of rehabilitation services, national measures should be considered one of the necessities of the health system. In addition to supporting the provision of social insurance for low-income families, this study sought to suggest an improved costing method for rehabilitation providers. The TDABC method can provide more realistic information on the cost structure and other valuable information, such as an overview of actual profit/loss and unused human capacity. It provides a basis for improving resource management for healthcare providers and increasing the cost-effectiveness of rehabilitation services. 

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of the University of Social Welfare and Rehabilitation Sciences (Code: USWR.REC.1399.123). 

Funding
This research was supported by the research project (No. 99-T-2496), funded by the University of Social Welfare and Rehabilitation Sciences.

Authors' contributions
Conceptualization and supervision: Mehdi Basakha; and Bijan Khorasani; Methodology: Mehdi Basakha;  and Seyed Mahdi Mohsenzadeh; Investigation, writing the paper: All authors; Data collection: Seyede Mahboobe Hosseini Zare, Seyed Mahdi Mohsenzadeh, Farzaneh Mohammadpour, and Marziyeh Izanloo; Data analysis: Mehdi Basakha; Funding acquisition and resources: Mehdi Basakha; Bijan Khorasani; Seyede Mahboobeh Hosseini, Seyed Mahdi Mohsenzadeh. 

Conflict of interest
The authors declared no conflict of interest.

Acknowledgments
This study would not have been possible without the contributions of the  Nezam Mafi Rehabilitation Center manager and staff, and for this, the authors  offer their sincere thanks.


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