1. Background

Nursing services have been traditionally regarded as free services included in medical services, so price competitions in nursing have been deemed to be unethical [1]. Even today, although a large part of medical services is performed by nurses, there are not many cases in which nursing services are classified as independent services and costs of the services are estimated or set. However, in modern society, health care services have been continuously growing with the development of scientific technologies, and medical needs have become diverse and complex due to demographic aging and socioeconomic changes, so the diversification and professionalism of services are also required in nursing as in other fields. Currently, nurses are trained professionals who have acquired systematic theories and skills and can fulfill health care needs. Therefore, nursing services include costs of training and maintenance of nursing workforce along with service production costs, so it is necessary to estimate costs for qualitative and quantitative contributions and expertise of nurses providing healthcare services [2]. In Korea, healthcare service costs are based on the price setting of the national health insurance system. Therefore, setting the costs of nursing services necessarily involves efforts to include relevant services at appropriate prices in the fee schedules of the national health insurance system.

In general, service costs are composed of monetary values and non-monetary elements. The costs of most health care services are measured by the human capital approach, and direct and indirect monetary values are reflected. The present fee schedule of the national health insurance system consists of the resource based relative value scale (RBRVS), and RBRVS are determined based on the workload of main service workforce and the degree of hazards in the workplace [3]. However, the human capital approach does not accurately reflect the values of healthcare services since it does not include intangible values, such as social and psychological costs and benefits of healthcare consumers arising from diseases, and the proportion of intangible values is relatively larger in the case of healthcare services, so an accurate assessment method is needed [4]. Since public services such as healthcare services are not traded in a market, it is very difficult for healthcare consumers to measure and evaluate the effects of services, so the method of identifying consumers' preferences for the needs and demand for healthcare services by a direct survey of willingness to pay (WTP) is mainly used [5].

WTP refers to the maximum amount of money that a consumer is willing to pay to reduce the risk of getting or contracting a disease [6] and it has the advantage of idealistically measuring the value of a product or service by quantifying both the tangible and intangible values of goods in currency. In foreign countries, WTP research is a concept that existed for quite a long time, and WTP studies in the field of healthcare services started in the 1970s and have been continuously carried out since then [7, 8]. In Korea, WTP research in healthcare services began in the field of nursing in the late 1990s. A study on the intention to use home health care in patients after hospital discharge published in 1999 investigated whether subjects have the intention to pay or not [9], and a study published in 2001 proposed a pricing policy reflecting the subjective value of consumers by applying the willingness to pay approach to the estimation of nursing service costs [1]. Since then, WTP research has been expanded to the fields of medical services and public health. However, there have not been many WTP research attempts in the field of nursing since the introduction of the studies. In health care services, reasonable allocation of limited resources is required. In modern society, very rapid technological development along with social and economic changes is leading to the continuous expansion of the area of health care services, and economic analysis to evaluate the social value for reasonable payment are gradually taking on greater importance [10]. This study attempted to examine WTP studies conducted in Korea to investigate the economic value of healthcare services perceived by consumers and analyze the research trends with a view to presenting useful basic data for finding directions for research with a willingness to pay approach in the field of nursing in the future.

2. Purpose

This study aimed to conduct a comprehensive review of trends in domestic studies applying WTP in the field of healthcare services in order to present the analysis results as reference data that can be applied and expanded to nursing policies and services in the future. The specific objectives of this study are as follows:

• to identify the general characteristics of WTP studies in healthcare services;

• to examine the status of each research field and area of WTP studies in healthcare services by year of publication;

• to investigate methods for deriving WTP and analysis methods in healthcare services.

1. Study Design

This study aimed to investigate the research trends in domestic studies on WTP in healthcare services and explore the status of research in the field of nursing. To review studies to investigate consumers' preferences and values regarding healthcare services and systems, this analysis was conducted by referring to the scoping review approach.

2. Study Procedure

This study was carried out according to the sequential steps of the scoping review framework proposed by Arksey and O'Malley [11].

1. Study Selection

A total of 40 studies were finally selected for this study. Initially, a total of 396 studies were extracted from domestic and foreign databases through the de-duplication process of removing duplicates from search results. The study titles and abstracts were first reviewed and this process was carried out according to the selection criteria. Theses, dissertations, and research reports were excluded during the first screening process. During the second selection process, after the full texts were obtained, selection and exclusion were made based on the content of the main text, and one study was included by hand searching. In the study selection process, studies which dealt only with intention to WTP were also included. Studies on the environment and health, health information data (personal health records), or mobile devices for health care services were not included (Figure 1).

Figure 1 Flow diagram of the study selection process. Click for larger image

2. General Characteristics

A total of 40 studies were selected for this study. They were published during the period from 1999 to 2020, and they consisted of 38 studies of willingness to pay (WTP) and 2 studies of willingness to accept (WTA) on healthcare systems or policies, medical interventions, disease treatment including therapeutic medicines or devices, disease prevention, and public health services or resources. The list and characteristics of selected studies are presented in Appendices 1 and 2. The studies analyzed in this review were cross-sectional studies to estimate the participants' perceived economic values and preferences for healthcare services. The selected studies included two studies which measured WTP as a component of exploratory research on the experience of using services, satisfaction with them, or intention to use services and three economic evaluation studies to measure benefits and the threshold of cost-effectiveness analysis. The question used for estimating WTP for services is generally an open-ended question which directly asks the price or requires respondents to present the reference price or the first bid price. Among studies which used techniques other than open-ended questions and did not present a specific price, one study examined willingness to pay for the price being co-payment and two studies asked respondents to select or present an additional cost as x% of the price currently paid for services. In addition, two studies investigated only whether the subjects were willing to pay or not without examining the specific price that the respondents were willing to pay.

3. Trends in WTP Research in Healthcare Services

Table 1 shows the fields and areas of WTP studies. When classifying studies according to the fields of healthcare services, studies whose field was difficult to define definitely were classified as those in medical services. As a result, among the selected studies, 24 studies were classified as researches in medical services, making up the largest proportion. In addition, seven studies in public health and five studies in nursing were included in this study. In terms of the publication year, it was found that the number of studies has been increasing since the late 2000s. Regarding specific research areas, research areas were divided into healthcare systems or policies, interventional services for disease treatment or prevention, and health management for health and disease management. There are 16 studies in the area of healthcare systems (policies), which are related to the introduction of new policies (systems) by period. As for research in the area related to direct interventions, 13 studies, including seven articles on medical services and four articles on educational and counseling services, were included. In the area of health management, 11 studies on disease prevention, health status improvement, or drug management programs were included.

Table 1 Fields of the Reviewed Researches Click for larger image

The examination of WTP studies by year of publication by dividing the years of publication into 5-year periods showed that although only 5 studies were published before 2006, the number of WTP studies was increased to 10 or more during each subsequent 5-year period. Regarding methods for deriving WTP, the method for deriving a WTP is to provide a general survey, a content valuation method (CVM) that utilizes virtual scenarios and a multi-attribute valuation method which require respondents to make choices between several attribute alternatives instead of directly asking them to report the monetary values of relevant services, were employed. Out of the three methods, CVM was used in 28 studies (70.0%). Between 2006 and 2010, 13 studies were conducted by various approaches. Regarding the survey techniques of CVM, open-ended (OE) questions, bidding games (BID), referendum questions, and dichotomous choice (DC) questions were applied. The OE question method has been used since the introduction of WTP research, and it was used alone or in combination with other techniques to derive WTP. BID was applied in seven studies before 2015. The DC question approach was used in 15 studies, out of which 12 studies employed double bounded dichotomous choice (DBDC) questions. Studies using DBDC questions accounted for the largest proportion, and the use of DBDC questions has been recently increasing. In 5 studies which applied the multi-attribute valuation method, conjoint analysis and the choice experiment method were used. Seven survey studies were identified (Table 2).

Table 2 Methods of Willingness to Pay Elicitation Click for larger image

Table 3 shows the status of the study population in the selected articles. 20 studies were conducted with the general population, while 20 studies specified participants as a particular demographic group. 17 out of the 20 studies were conducted with patients, and the participants of the other 3 studies were patients and their guardians, caregivers of patients, and participants in an interventional program, respectively. As for the studies conducted with the general population, the sample size was over 500 in 14 studies, and 4 out of the 14 studies were conducted with 1500 or more people. In the case of the studies of patients, the sample size was 500 or less in 18 studies.

Table 3 Subjective Status of Included Studies Click for larger image

With respect to data collection methods, data collection was carried out by interviews in 27 studies, by a self-report survey in 8 studies, and by interviews and a self-report survey according to the participants in 1 study. As to interview methods, face-to-face interviews and telephone interviews were used in 24 studies and 3 studies, respectively. Self-report methods included the method of data collection by a web-based survey using the Internet. Data collection methods were not clearly specified in 4 studies (Table 4).

Table 4 Methods of Data Collection Click for larger image

The data analysis methods consisted of descriptive statistics to summarize data, identification of factors influencing WTP, and the estimation of WTP for closed questions. The independent variables for identifying influencing factors included the general characteristics of participants (demographic and socioeconomic variables), health status and disease conditions related to the research subject, and variables specific to the research subject. The probit model and survival analysis were applied to estimate WTP. Logistic regression analysis was used to identify factors influencing intention to WTP, and linear regressing analysis, including simple linear, multiple linear, and multivariate regression analysis, were performed to determine the relationship between independent variables and the dependent variable, WTP. In some studies, t-test, ANOVA, χ² test, and correlation analysis were also conducted to compare differences between groups for the dependent variable.

4. WTP Studies in the Field of Nursing

Five WTP studies in nursing were found in this study. Regarding the year of publication, they were respectively published immediately before and after 2000, in 2010, in 2019, and in 2020. With respect to the research subject, they were composed of a research on early home visiting nursing services, a study conducted to present the policy suggestion that the intangible values of consumers should be reflected in the price setting of nursing services, a research on cognitive enhancement programs for older people, and a study of the telephone education and counseling services of advanced practice nurses (APNs) on the nursing of critically ill patients and self-care of breast cancer patients. As for the study population, in studies published before 2011, participants were patients (or their family) or older people who participated in a program, while studies published since 2011 were conducted in the general population. In both the two studies of the general population, the sample size was 500 or more. To derive WTP, CVM was applied in 4 studies published since 2000. Among them, Ko & Park [1] examined differences between the results obtained using OE question, BID and referendum question techniques. Lim et al.[13] used the OE question technique in combination with the referendum question. Studies conducted after 2019 employed DBDC questions. As for the survey methods, face-to-face interviews were used in 2 studies, and a web-based data collection method was used in 2 studies, but the data collection method was not specified in 1 study (Appendix 2).