Analysis of Research Trends on Older Adults with Hearing Loss in Korea: Using the ICF Core Set

Soo Jin Cho; Mi Sook Lee; Yu Ri Lee

doi:10.21848/asr.230130

Audiology and Speech Research > Volume 20(1); 2024 > Article

Cho, Lee, and Lee: Analysis of Research Trends on Older Adults with Hearing Loss in Korea: Using the ICF Core Set

Research Paper

Audiol Speech Res 2024;20(1):6-17.

Published online: January 31, 2024

DOI: https://doi.org/10.21848/asr.230130

Analysis of Research Trends on Older Adults with Hearing Loss in Korea: Using the ICF Core Set

Soo Jin Cho¹

, Mi Sook Lee²

, Yu Ri Lee³

¹Department of Speech-Language Pathology, Nambu University, Gwangju, Korea

²Faculty of Social Welfare and Rehabilitation, Kaya University, Gimhae, Korea

³Department of Social Welfare, Nambu University, Gwangju, Korea

Correspondence: Yu Ri Lee, PhD Department of Social Welfare, Nambu University, 1 Nambudaegil, Gwangsan-gu, Gwangju 62271, Korea
Tel: +82-62-970-0135 Fax: +82-62-970-0049 E-mail: yrlee@nambu.ac.kr

Received October 24, 2023 Revised December 26, 2023 Accepted December 29, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

This study aimed to analyze trends of research on older adults with hearing loss, based on the framework of the International Classification of Functioning, Disability and Health (ICF) core set for hearing loss in Korea, and to present implications for the direction and challenges of research on older adults with hearing loss in the future.

Methods

A total of 54 studies related to older adults with hearing loss, published in academic journals from 2000 to July 2023 in Korea, were analyzed.

Results

In the analysis of research methods, quantitative studies accounted for 97.0%, among which survey studies accounted for 56.7%, more than experimental studies. As a result of the analysis by research theme, studies related to ‘quality of life and satisfaction (21.1%)’ and ‘psychological and emotional characteristics (18.3%)’ were frequent. As a result of the analysis by the classification of the ICF core set, among the components of the ICF, studies related to ‘activities and participation’ and ‘body functions’ were the most. By subcategory, ‘hearing functions (12.0%)’ and ‘emotional functions (11.7%)’ of the body functions sub-area, and ‘listening (10.9%)’ of the activities and participation subarea were frequent.

Conclusion

The results of this study will be useful as a foundational reference for the evaluation of hearing impairments of older adults with hearing loss, the development of hearing rehabilitation programs, and the establishment of various health and welfare policies.

International Classification of Functioning, Disability and Health (ICF), ICF core set, Older adults with hearing loss, Research trends

INTRODUCTION

According to ‘2022 Statistics on older adults’ by Statistics Korea, the number of older adults aged 65 and over in Korea was 9.018 million, accounting for 17.5% of the total population. It is expected to increase to 20.6% by 2025, 3 years later, and Korea is expected to enter a super-aged society. As Korea enters a super-aged society, in addition to economic problems caused by the decline in the workingage population, age-related health problems such as chronic diseases, dementia, and decreased physical function are becoming important. Among them, age-related hearing loss (presbycusis) is one of the three most common chronic conditions in old age, along with arthritis and hypertension, and it is increasing worldwide. In particular, age-related hearing loss mainly causes communication difficulties due to hearing loss in the high-frequency band, and has a negative impact on interpersonal relationships and overall daily life, causing stress, anxiety, and depression (Chun et al., 2005; Herbst & Humphrey, 1980; Kalayam et al., 1991). In addition, since hearing is related to cognitive functions such as memory and thinking, the risk of dementia may increase due to the deterioration of memory and cognitive function as the degree of hearing loss in older adults becomes more severe (Lemke & Scherpiet, 2015; Loughrey et al., 2018). In the past, hearing loss was recognized only as a communication limitation problem for individuals with difficulty communicating. Recently, it has been recognized as an important disease that seriously undermines the quality of life of older adults by causing various problems such as loss of self-confidence, withdrawal from social activities, psychological alienation, depression, and anxiety, including deterioration of cognitive ability, and causes behavioral disorders and social and psychological disorders related to communication (Chae, 2011; Chung, 2020). Therefore, to comprehensively evaluate how hearing loss in old adults affects various areas such as communication, daily life, and social participation, and to plan and manage individualized hearing rehabilitation interventions, it is necessary to take a multifaceted approach that can improve the quality of life by considering not only the recovery of the physical abilities but also the functional aspects.

From these perspectives, it is necessary to consider the World Health Organization (WHO)’s International Classification of Functioning, Disability and Health (ICF) model to address various health problems, including hearing loss in older adults. The ICF model is an international classification system developed to be applied to various aspects of health. While the existing classification system related to disability mainly focused on the cause or diagnosis of disability, the ICF is a concept created by the need to evaluate and analyze disability from a more functional and integrated perspective (Shin, 2013). It was also introduced to understand disability not only as a health problem but as a result of interaction with environmental and personal factors, including the functional status of an individual, and to provide a universal language and framework for systematically describing and classifying functions and disorders related to health conditions (Hwang, 2004). The ICF model’s conceptual framework is divided into two main domains: functioning & disability and contextual factors. ‘Function and disability’ is again ‘divided into body functions and structures’ and ‘activities and participation’, and ‘contextual factors’ are divided into ‘environmental factors’ and ‘personal factors’, composing four components. Each component interacts with each other to represent health and health-related conditions (Ko et al., 2012). In addition, the WHO has developed an ICF core set, which is a core item that can represent functional impairment in specific health conditions or medical situations, centered on ICF, and the ICF core set for hearing loss consists of 117 comprehensive categories and 27 brief categories (Danermark et al., 2013). The brief categories are an abbreviated form of the most important higher functions and conditions among the comprehensive categories, so it is highly relevant to specific health conditions and are easy to use in the clinical field because they provide only important information.

As for previous studies related to the ICF in Korea, there are studies on surveys of people with disabilities and comparing ICF items (Kang et al., 2013), analysis of research trends related to college students with disabilities in Korea using ICF framework (Park et al., 2020), and evaluation of disability (Cho, 2020). In addition, studies on ICF related to older adults are also increasing, such as the quality of life of older adults (So et al., 2011), the promotion of physical activity in older adults with physical disabilities (Koo et al., 2017), and the intervention of older adults with dementia (Kwak et al., 2022). A study using the ICF core set for hearing loss was also conducted. Oh(2015) reported that developing an integrated questionnaire in the area of hearing loss in Korea based on ICF can help build information and provide tailored rehabilitation services related to functional impairment, restriction of activities, and support for people with hearing disabilities. In addition, since there is almost no basic and applied research on ICF in audiology in Korea, it emphasized that to materialize the use of ICF, the need to expand awareness of ICF centered on experts in audiology and related studies is increasing. In this way, the ICF’s conceptual framework, which looks at health and disability from the perspective of not only physical and mental conditions but also activities, social participation, and the interaction between the individual and the environment, can be a useful perspective for assessing the health and welfare needs of older adults. Therefore, looking at hearing loss in older adults by applying the ICF core set classification will help comprehensively understand the impact on various areas such as psychological and emotional state, activities of daily living, and social participation and communication of older adults to find ways to improve them.

This study aimed to analyze the research trends related to older adults with hearing loss from various angles using the ICF core set for hearing loss and use the results as basic data for the development and application of hearing impairment-related evaluation scales and aural rehabilitation programs for older adults with hearing loss and provide implications for the direction and challenges for related research in the future. In addition, we aimed to contribute to the establishment of various health and welfare policies to expand social participation and improve access rights for older adults with hearing loss.

MATERIALS AND METHODS

Selection of studies for analysis

To analyze research trends related to older adults with hearing loss in Korea, studies published in the registered (candidate) journals of the Korea Citation Index (KCI) were included for analysis, and studies from 2000, when Korea entered the ‘aging society’ to the latest period were analyzed. As of the end of July 2023, the data search was conducted using the databases DBpia, SCHOLAR, RISS, KCI, and KISS, which can search for academic data in Korea. The keywords were searched by combining these words interchangeably; ‘aging’, ‘older adults’, ‘old age’, ‘elderly’, ‘aged’ and ‘presbycusis’, ‘hearing loss’, ‘hearing impairment’.

The specific selection processes were as follows. First, master’s and doctoral dissertations, conference proceedings that are highly likely to be duplicated in academic journals, and research reports were excluded. Only papers published in the registered (candidate) journals of KCI were included and a total of 562 studies were searched in this first round. Second, studies that do not fit this study’s topic were excluded from the first selected studies. Fact-finding surveys, trend studies, and review studies were also excluded from the analysis because it was judged that these studies were difficult to apply to the ICF core set (Park et al., 2020). Through this second round, 78 studies were selected. Third, among the studies selected in the second round, 54 studies on older adults over 65 with hearing loss were included in the final analysis. This is based on the fact that the WHO has set the entry age for older adults at 65 years old when presenting the criteria for an aging society (Lim & Chae, 2011), and several domestic laws, including the Welfare of Senior Citizens Act, also provide welfare benefits for older adults based on the age of 65.

Analysis criteria and topics

In this study, to examine the research trends related to older adults with hearing loss, we divided the analysis into general research trends that applied the analysis criteria of the year of publication, research methods, and research topics, and research trends that applied the ICF core set for hearing loss. The specific analysis criteria are as follows.

First, in the analysis of general research trends, the publication year was examined for the overall year-overyear changes for studies published from 2000 to the end of July 2023 in registered (candidate) journals in Korea (Kim & Ko, 2023). The research methods were largely divided into quantitative and qualitative research. Quantitative research was further divided into experimental and survey research (Sung & Si, 2020), and the cases in which both research methods were included were treated as duplicates. Finally, research topics can be categorized in various ways depending on the researcher. In this study, the research topics were derived based on the dependent variable of the included studies (Hwang, 2015) and then categorized into similar topics. As a result, a total of eight subject areas (clinical characteristics of hearing loss, subjective perception of hearing loss, hearing aids, intervention program, speech recognition and communication, quality of life and satisfaction, psychological and emotional characteristics, and daily life) were derived (Table 1). The cases in which the included studies had multiple topics were treated as duplicates.

Second, in the analysis of research trends using the ICF core set, the brief ICF core set for hearing loss was compared with the research topics of the analyzed studies. In the case of the survey study, the contents of each questionnaire related to the research topic were analyzed by comparing with the brief ICF core set (Oh, 2015). In addition, if the analyzed studies dealt with various subcategories of the brief ICF core set, duplication is allowed, and all components are included.

Data analysis and inter-researcher reliability

The data collected were coded according to the analysis criteria, such as year of publication, research methods, research topics, and ICF core set classification, and then the frequency and percentage of the studies analyzed were calculated using SPSS version 23 (IBM Corp., Armonk, NY, USA) software. Three researchers independently analyzed the studies according to the analysis criteria. Then, they calculated the inter-researcher reliability by dividing the number of matching studies by the total number of studies (Park et al., 2020). As a result, the inter-researchers reliability was about 93.8%.

RESULTS

Analysis of general research trends

Results according to the year of publication

As a result of analyzing the trends by publication year (Table 2), research on older adults with hearing loss was conducted intermittently from 2000 to 2009 but has become a continuous pattern since 2010, and 48 out of 54 studies (88.9%) were published after 2010. In addition to the six studies published in 2012, six were published in 2016 and seven in 2017, indicating that research was actively conducted in these 2 years.

Results by research methods

The research methods were largely divided into quantitative research (experimental and survey research) and qualitative research. In cases where both research methods were applied in a study, they were classified by including each in its respective research method (Table 3). The analysis showed that 65 (97.0%) out of the total were quantitative studies, which was significantly more than 2 (3.0%) qualitative studies. Among the quantitative studies, 38 (56.7%) were survey studies, and 27 (40.3%) were experimental studies, indicating a greater proportion of survey studies. Looking at the year by year, experimental and survey studies, which are quantitative, have shown an increase since 2010, with the largest number of survey studies in 2016 and 2017, with five survey each. On the other hand, qualitative studies were published in 2019 and 2022, one each.

Results by research topics

The research topics were categorized based on the dependent variable of the studies under analysis, grouping similar topics together. In cases where a study covered multiple research topics, they were classified by including each in its respective research topic (Table 4). The analysis showed that 15 (21.1%) were related to ‘quality of life and satisfaction’, followed by 13 (18.3%) ‘psychological and emotional characteristics’, and 11 (15.5%) ‘clinical characteristics of hearing loss’ and ‘speech recognition and communication’ for each. On the other hand, topics related to ‘hearing assistive devices’ and ‘daily life’ had the lowest proportion, with 5 (7.0%) and 3 (4.2%).

Analysis of research trends by the ICF core set classification

The ICF core set classification was analyzed, based on the brief ICF core sets for hearing loss. In cases where a study covered multiple subcategories of the ICF core set, they were classified by including each in its respective subcategory (Table 5). The analysis showed that the most common ICF component was ‘activities and participation’, with 125 (47.0%), followed by ‘body functions’ with 103 (38.7%), ‘environmental factors’ with 36 (13.5%), and ‘body structures’ with 2 (0.8%).

As a result of the analysis by subcategory, in the body functions area, ‘hearing functions (b230)’ of ‘sensor functions and pain’ had the highest number of 32 studies (12.0%), followed by ‘emotional functions (b152)’ of ‘mental functions’ with 31 (11.7%). On the other hand, ‘seeing functions (b210)’ and ‘sensations associated with hearing and vestibular function (b240)’ appeared in 1 (0.4%) each, indicating that little research has been conducted on these components. In the body structures area, only 1 (0.4%) each was identified for the ‘structure of middle ear (s250)’ and ‘structure of inner ear (s260)’ of ‘the eye, ear, and related structures’. In the activities and participation area, ‘listening (d115)’ of ‘learning and applying knowledge’ was the most common with 29 (10.9%), followed by ‘communicating with-receivingspoken messages (d310)’ and ‘using communication devices and techniques (d360)’ of ‘communication’ with 18 (6.8%) each. However, ‘school education (d820)’ was not discussed in the analyzed studies. Finally, in the area of environmental factors, ‘sound (e250)’ of ‘natural environment and humanmade changes to environment’ and ‘products and technology for communication (e125)’ of ‘products and technology’ had the highest number of studies with 14 (5.2%) and 13 (4.9%), respectively, and ‘individual attitudes of immediate family members (e410)’ and ‘societal attitudes (e460)’ were not discussed in the analyzed studies.

DISCUSSIONS

This study aimed to analyze research trends related to older adults with hearing loss in Korea from various perspectives, focusing on the ICF core set classification. It used the results as basic data for developing and clinically applying hearing impairment-related evaluation scales and hearing rehabilitation programs for older adults with hearing loss. It also aimed to suggest implications for the future direction and challenges of related research. The discussions on major research results are as follows.

First, as a result of the analysis according to the year of publication for the general research trends, research on older adults with hearing loss published after 2010 accounted for about 90% of the total number of papers, and in particular, six papers were published in 2016 and seven in 2017, indicating that research was actively conducted for 2 years. It is determined that this is related to the social phenomenon that Korea entered an aging society in 2000 and then entered an aged society in 2017 at an unprecedented speed. In other words, it seems that many related studies have emerged as the seriousness of various socio-economic problems caused by the aging of the population and the consideration of policy measures to prepare necessary policies has increased. However, since 2018, the number of published papers has shown a slight decline, and it is important to prepare policies through multifaceted research on older adults with disabilities, including hearing loss, which is socially disadvantaged, as the country is about to enter a super-aged society in 2025 (Lim & Kim, 2022).

As a result of the analysis according to the research method, 97.0% out of the total 58 studies were quantitative research, which was significantly more than qualitative research. Research related to older adults with hearing loss was mainly quantitative research, despite the need for both quantitative research to understand the clinical characteristics of hearing loss and its effects and to verify the effects of various interventions, including hearing rehabilitation, and qualitative research to analyze the experiences and needs of older adults with hearing loss in depth. This pattern is similar to the phenomenon in which many studies in various fields, including health care, have adopted quantitative research that applies statistical analysis to derive the association and outcome of variables (Chung & Cho, 2008). In the future, it is necessary to actively utilize qualitative research methods to investigate subjective perceptions, empirical considerations, and various new problems of older adults with hearing loss through an indepth understanding of the aging process in related research. Among quantitative studies, survey studies accounted for 56.7%, and experimental studies accounted for 40.3%, which is different from the results of a study by Lee & Seo(2016), which accounted for more than 80% of experimental studies. This is speculated to be the result of including journal articles from various academic disciplines, such as social welfare, nursing, and education, including audiology, in the analysis. Finally, as a result of the analysis according to the research topic, the most frequent research topic was related to ‘quality of life and satisfaction,’ accounting for 21.1%. This seems to be related to the social phenomenon that the influence of older adults’ quality of life on the entire society in Korea is increasing due to the rapid increase in the elderly population. In the included studies, studies related to ‘quality of life and satisfaction’ were about the quality of life according to the degree of hearing loss (Shin, 2012) and the relationship between hearing aid wearing and satisfaction and quality of life in older adults with hearing loss (Park & Oh, 2022; Park & Park, 2017; Son & Heo, 2018), the effect of lifestyle and social environment satisfaction on the life satisfaction of older adults with hearing loss (Jeong et al., 2022), and factors related to the quality of life of older adults with hearing loss (Han, 2021). However, many studies used tools to assess the overall quality of life, such as the World Health Organization Quality of Life Scale, to assess the quality of life of older adults with hearing loss, so we believe that there may be limitations in understanding the specific impact of hearing loss-related factors such as lack of communication or disconnection on quality of life. In this regard, it is significant that the Quality of Life in Adult and Elder with Hearing Loss (QOL-AEHL) has been developed (Park & Kim, 2017), which can evaluate the quality of life of adults and old adults with hearing loss, and follow-up studies on the standardization and application of related scales should be carried out continuously in the future. The second most common research topic was ‘psycho-emotional characteristics,’ with 13 papers (18.3%). Many were related to depressive emotions, such as the effects of hearing loss on the depressive tendency in older adults with hearing loss (Chun et al., 2005), depression and cognitive function (Kim et al., 2015), depression and self-efficacy (Lee & Ha, 2019), and subjective memory impairment and depression (Lee, 2016). On the other hand, previous studies reported that the incidence of dementia in older adults with hearing loss was about 1.9~4.9 times higher than that of older adults with normal hearing (Lin et al., 2011), and age-related hearing loss can be a predictor of dementia (Loughrey et al., 2018). As this study did not include research on the link between hearing loss and dementia in older adults, various research on this topic needs to be conducted in the future. In addition, studies on ‘clinical characteristics of hearing loss’ and ‘speech recognition and communication’ accounted for 15.5%, ‘subjective perception of hearing loss’ 9.9%, and intervention programs 8.5%, respectively. On the other hand, the subjects related to ‘hearing assistive devices’ and ‘daily life’ showed a relatively low proportion of studies at 7.0% and 4.2%, respectively. In the case of hearing aids and cochlear implants, it can be inferred as a result of reflecting the fact that the analysis criteria for the research topic in this study were set only as dependent variables, and the number of cochlear implant cases for older adults among hearing aids was limited compared to other age groups. However, in recent years, the number of cochlear implants for people with hearing loss in their 60s and older and older adults has increased rapidly compared to the past, and the impact on the use of hearing aids by older adults is diverse (Lee, 2013). It is necessary to expand and apply the concept of auditory reward and hearing rehabilitation through hearing aids to the holistic perspective of older adults with hearing loss, such as communication, mental, emotional, and social aspects, quality of life, and in-depth research in related fields should be conducted.

Second, as a result of the analysis according to the brief ICF core set for hearing loss, ‘activities and participation’ and ‘body functions’ accounted for 47.0% and 38.7%, respectively, which was more than 85% of the total, followed by ‘environmental factors’ at 13.5% and ‘body structures’ at 0.8%. It is speculated that the proportion of the ‘activities and participation’ is higher than other items because it is directly related to the individual’s work or behavior execution and actual life and can be an important limiting factor in communication problems related to hearing loss (Shin et al., 2012). On the other hand, ‘environmental factors’ are also related to the sub-components of ‘activities and participation’ and are variables that greatly influence social participation (Kim & Kim, 2015). Still, as a result of this study, little research has been conducted in this field. In the future, to expand social participation and improve access rights of older adults with hearing loss, it will be necessary to create an appropriate environment and have more active discussions in this area. Few studies related to ‘body structures’ have been conducted, which can be interpreted as a result of the fact that research on older adults with hearing loss has focused on the recovery and rehabilitation of various functions, including hearing, as most cases of age-related hearing loss present a pattern of sensorineural hearing loss that is difficult to recover from (Choi & Chung, 2011).

In the subcategory analysis, ‘hearing functions (b230)’ and ‘emotional functions (b152)’ of body functions were most common at 12.0% and 11.7%, respectively, while ‘seeing functions (b210)’ and ‘sensations associated with hearing and vestibular function (b240)’ such as tinnitus or dizziness were rarely studied. Patients with age-related hearing loss often complain of tinnitus in the upper register (Gopinath et al., 2010), and tinnitus in older adults not only reduces the quality of life but also affects memory and attention and is also known as an independent risk factor for depression (Michikawa et al., 2013). However, since tinnitus is often overlooked because it is considered a natural consequence of the aging process (Lee & Lee, 2007), tinnitus evaluation and rehabilitation should be fully considered when planning a hearing rehabilitation program for older adults with hearing loss in the future. In the area of body structures, only the ‘structure of middle ear (s250)’ and ‘structure of inner ear (s260)’ items were found to be related, but there were few studies on them. In the activities and participation area, ‘listening (d115)’ was the most common at 10.9%, and ‘communicating with-receiving-spoken messages (d310)’ and ‘using communication devices and techniques (d360)’ were the most common at 6.8%, respectively. Lastly, the environmental factors area was closely related to the activities and participation, and ‘sound (e250)’ and ‘products and technology for communication (e125)’ were high. However, the ‘individual attitudes of immediate family members (e410)’ and ‘societal attitudes (e460)’, which correspond to ‘attitudes’, were not covered in the studies analyzed in this study. These results differ from Shin et al.(2012) study, which found that ‘attitudes’ were the most influential factor among environmental factors. Therefore, when developing evaluation scales and hearing rehabilitation programs related to hearing impairment, it is necessary to select a balanced research topic and organize variables so that items related to family members and social attitudes can be reflected.

The conclusions and suggestions of this study are as follows. First, research has been conducted continuously since 2010 by publication year, and it was most active in 2016~2017. Second, most studies used quantitative research methods, and only a few studies were conducted using qualitative methods. Therefore, based on an indepth understanding of the aging process, it is necessary to actively use qualitative research methods to identify subjective perceptions and empirical considerations of older adults with hearing loss and various new problems. Third, although the most common research topic was ‘quality of life and satisfaction’, most studies used a scale to evaluate the overall quality of life of older adults with hearing loss, so it is limited to specifically grasp the impact of factors such as lack of communication or disconnection due to hearing loss on the quality of life. Therefore, there is a need for standardizing quality-of-life assessment scales that reflect the characteristics of older adults with hearing loss and followup studies to apply it. In addition, among the ‘psychological and emotional characteristics’, ‘dementia’, ‘hearing assistive devices’ and ‘daily life’ of older adults with hearing loss have a relatively low proportion of research, so given the importance of related topics, various in-depth studies should be conducted in the future. Third, although there were many ICF components related to ‘activities and participation’ and ‘body functions’ in the analysis of the results according to the brief ICF core set for hearing loss, more active discussions on ‘environmental factors’ are needed to expand social participation and ultimately improve the quality of life of older adults with hearing loss. In the analysis by subcategory, the body functions area had the most components related to ‘hearing function’ and ‘emotional functions’. In contrast, as ‘sensations associated with hearing and vestibular function’ such as tinnitus and dizziness were rarely studied, this area needs to be discussed in the future. Besides that, environmental factors had a lot of components related to ‘sound’ and ‘using communication devices and techniques’. There were no studies on family members or social attitudes, even though family members or social attitudes are important environmental factors, so it is necessary to constitute components related to family members and social attitudes to be reflected in the evaluation of older adults with hearing loss and the development of hearing rehabilitation programs.

There are a few limitations in this study. First, when selecting the analysis papers, only studies on older adults over 65 with hearing loss from the registered (candidate) journals of KCI were included, so there is a limitation in analyzing the overall research trend of older adults with hearing loss. Especially due to the rapid aging phenomenon in Korea, there are various perspectives regarding the age criteria for older adults. Therefore, in follow-up studies, it is necessary to conduct additional analysis by expanding the age criteria for older adults and the scope of the research papers to include various sources such as overseas journals. Second, the discussion focused on the quantitative aspect of the analysis of the results according to the ICF core set may be insufficient for an in-depth understanding of the research trends related to older adults with hearing loss, so it is necessary to expand the scope of analysis of future research results and look at them from various aspects. Third, as the criteria of the research topic were categorized based on the dependent variable, it is necessary to consider this part when interpreting the research results to understand the results of the research trend. Finally, this study did not systematically follow the ‘preferred reporting items for systematic reviews and meta-analysis (PRISMA) statement’ in the procedure for selecting papers. Therefore, there is a need to supplement this aspect this aspect in future research. Nevertheless, this study is significant in that it provided implications for the direction and challenges related to future research by comprehensively examining research trends related to various functional areas such as daily life activities and social participation as well as communication of older adults with hearing loss by using the brief ICF core set item for hearing loss for the first time as an analysis framework. In addition, the results of this study will be useful as a foundational reference for the evaluation of older adults with hearing loss, the development of hearing rehabilitation programs, and the establishment of various health and welfare policies.

Notes

Ethical Statement

N/A

Declaration of Conflicting Interests

There is no conflict of interests.

Funding

N/A

Author Contributions

Conceptualization: Soo Jin Cho, Mi Sook Lee, Yu Ri Lee. Data curation: Soo Jin Cho. Formal analysis: Soo Jin Cho, Mi Sook Lee, Yu Ri Lee. Investigation: Soo Jin Cho, Mi Sook Lee, Yu Ri Lee. Methodology: Soo Jin Cho, Mi Sook Lee, Yu Ri Lee. Writing—original draft: Soo Jin Cho, Mi Sook Lee. Writing—review & editing: Soo Jin Cho, Mi Sook Lee, Yu Ri Lee. Approval of final manuscript: all authors.

Acknowledgments

N/A

Table 1.

Research topics and details

Research topics	Details
Clinical characteristics of hearing loss	Risk factors and diseases related to hearing loss, identification of the degree and types of hearing loss, development, and verification of subjective evaluation scale for hearing loss
Subjective perception of hearing loss	Perception and experience of hearing loss, Hearing Handicap Inventory for the Eldely
Hearing assistive devices	Use and satisfaction of hearing aids, cochlear implant
Intervention program	Aural rehabilitation, art therapy, horticultural activities
Speech recognition and communication	Recognition and perception of consonants/vowels, monosyllables, bisyllables and sentences, communication
Quality of life and satisfaction	General quality of life and satisfaction, quality of life-related to communication and hearing impairment, life satisfaction
Psychological and emotional characteristics	Depression, memory and cognition, loneliness, self-efficacy
Daily life	Activities and performance of daily living

Table 2.

Studies by the year of publication

	‘00	‘01	‘02	‘03	‘04	‘05	‘06	‘07	‘08	‘09	‘10	‘11	‘12	‘13	‘14	‘15	‘16	‘17	‘18	‘19	‘20	‘21	‘22	‘23	Total
Number of studies	1	1	1	0	1	1	0	0	1	0	3	2	6	2	2	3	6	7	3	3	3	4	4	0	54

Table 3.

Studies by research methods

Category	‘00	‘01	‘02	‘03	‘04	‘05	‘06	‘07	‘08	‘09	‘10	‘11	‘12	‘13	‘14	‘15	‘16	‘17	‘18	‘19	‘20	‘21	‘22	‘23	Total^*
Quantitative studies
Experimental studies	0	0	1	0	0	1	0	0	1	0	2	0	3	1	2	3	2	3	1	0	3	2	2	0	27 (40.3)
Survey studies	1	1	1	0	1	1	0	0	0	0	2	2	4	1	1	1	5	5	2	2	2	3	3	0	38 (56.7)
Qualitative studies	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0	1	0	2 (3.0)
Total	1	1	2	0	1	2	0	0	1	0	4	2	7	2	3	4	7	8	3	3	5	5	6	0	67 (100.0)

Values are presented as number (%).

^* Duplicated research methods are included

Table 4.

Studies by research topics

Category	‘00	‘01	‘02	‘04	‘05	‘08	‘10	‘11	‘12	‘13	‘14	‘15	‘16	‘17	‘18	‘19	‘20	‘21	‘22	Total^*
Clinical characteristics of hearing loss	1	1	1	0	0	0	2	1	0	0	1	0	2	1	0	0	0	0	1	11 (15.5)
Subjective perception of hearing loss	0	0	1	0	0	0	0	0	1	0	0	0	0	1	0	1	1	1	1	7 (9.9)
Hearing assistive devices	0	0	0	0	0	0	0	0	1	1	0	1	0	0	0	1	0	0	1	5 (7.0)
Speech recognition and communication	0	0	0	0	0	1	1	0	2	0	1	1	1	2	0	0	1	1	0	11 (15.5)
Intervention program	0	0	0	0	0	0	0	0	0	1	0	1	0	0	1	1	1	1	0	6 (8.5)
Quality of life and satisfaction	0	0	0	1	0	0	0	0	2	0	0	1	1	2	2	0	1	2	3	15 (21.1)
Psychological and emotional characteristics	0	0	0	1	1	0	0	1	2	0	0	2	2	1	0	1	1	1	0	13 (18.3)
Daily life	0	0	0	0	0	0	0	0	1	0	0	0	0	1	0	1	0	0	0	3 (4.2)
Total	1	1	2	2	1	1	3	2	9	2	2	6	6	8	3	5	5	6	6	71 (100.0)

Values are presented as number (%).

^* Duplicated research topics are included

Table 5.

Studies by the brief ICF core set for hearing loss

Component	1st level	ICF category titles (ICF code)	‘00	‘01	‘02	‘04	‘05	‘08	‘10	‘11	‘12	‘13	‘14	‘15	‘16	‘17	‘18	‘19	‘20	‘21	‘22	Total^*
Body functions	Mental functions	Temperament and personality functions (b126)	1	1	1	1	0	0	2	1	3	0	0	2	1	3	2	1	2	1	2	24 (9.0)
		Attention functions (b140)	0	0	0	0	0	0	0	1	2	0	0	1	2	0	2	0	0	0	1	9 (3.3)
		Memory functions (b144)	0	0	0	0	0	0	0	1	1	0	0	1	2	0	0	0	0	0	0	5 (1.9)
		Emotional functions (b152)	1	1	1	1	1	0	2	2	3	0	0	2	2	4	2	1	2	3	3	31 (11.7)
	Sensor functions and pain	Seeing functions (b210)	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	0	0	1 (0.4)
		Hearing functions (b230)	1	1	1	0	0	1	3	1	4	2	2	1	3	3	2	1	2	2	2	32 (12.0)
		Sensations associated with hearing and vestibular function (b240)	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	1 (0.4)
Body structures	Structure of the nervous system	Structure of brain (s110)	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
	The eye, ear, and related structures	Structure of external ear (s240)	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
		Structure of middle ear (s250)	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	0	1 (0.4)
		Structure of inner ear (s260)	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	0	0	0	0	1 (0.4)
Activities and participation	Learning and applying knowledge	Listening (d115)	1	1	1	0	0	1	3	1	4	1	1	1	2	4	1	1	2	1	3	29 (10.9)
	General tasks and demands	Handling stress and other psychological demands (d240)	1	1	1	0	0	0	2	1	3	0	0	0	0	1	0	0	1	0	0	11 (4.2)
	Communication	Communicating with - receiving - spoken messages (d310)	1	1	1	0	0	0	2	2	1	0	1	0	0	4	1	0	1	2	1	18 (6.8)
		Conversation (d350)	1	1	1	0	0	0	2	1	1	0	1	0	0	4	0	0	1	1	1	15 (5.6)
		Using communication devices and techniques (d360)	1	1	1	0	0	0	2	1	2	1	1	1	0	3	0	1	1	0	2	18 (6.8)
	Interpersonal interactions and relationships	Family relationships (d760)	1	1	1	1	0	0	2	1	1	0	0	0	0	4	0	0	1	1	1	15 (5.6)
	Major life areas	School education (d820)	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
	Major life areas	Remunerative employment (d850)	0	0	0	1	0	0	0	0	1	0	0	1	1	0	2	0	0	0	1	7 (2.6)
	Community, social and civic life	Community life (d910)	1	1	1	0	0	0	2	1	1	0	0	0	0	2	0	0	1	0	2	12 (4.5)
Environmental factors	Products and technology	Products and technology for communication (e125)	1	1	1	0	0	0	2	1	2	1	0	0	0	1	0	1	1	0	1	13 (4.9)
	Natural environment and human-made changes to environment	Sound (e250)	1	1	1	0	0	0	2	1	2	0	1	0	0	2	1	0	1	0	1	14 (5.2)
	Support and relationships	Immediate family (e310)	0	0	0	0	0	0	1	0	0	0	0	0	0	0	0	0	0	0	0	1 (0.4)
	Support and relationships	Health professionals (e355)	0	0	0	0	0	0	0	0	1	0	0	0	0	0	0	0	0	0	1	2 (0.8)
	Attitudes	Individual attitudes of immediate family members (e410)	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
	Attitudes	Societal attitudes (e460)	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
	Services, systems, and policies	Health services, systems and policies (e580)	0	0	0	0	0	0	0	0	1	0	0	1	1	0	2	0	0	0	1	6 (2.2)
Total			12	12	12	4	1	2	27	16	33	5	8	11	15	36	15	6	16	11	24	266 (100.0)

Values are presented as number (%). ICF: International Classification of Functioning, Disability and Health.

^* Duplicated subcategories of the ICF core set are included

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