NIDCD Working Group on Accessible and Affordable Hearing Health Care for Adults with Mild to Moderate Hearing Loss
August 25-27, 2009
The National Institute on Deafness and Other Communication Disorders/National Institutes of Health (NIDCD/NIH) sponsored a working group on Accessible and Affordable Hearing Health Care for Adults with Mild to Moderate Hearing Loss on August 25-27, 2009. The working group was held in Bethesda, Maryland. The purpose of the working group was to develop a research agenda to increase accessibility and affordability of hearing health care for adults with mild to moderate hearing loss, including accessible and low cost hearing aids.
Hearing loss (HL) is a public health issue and is among the leading public health concerns. Approximately 17 percent of American adults, or 36 million people, report some degree of HL1. HL is the third most prevalent chronic health condition facing seniors2. Fewer than 20 percent of those with HL who require intervention and treatment seek help for their condition3. Untreated HL has social and economic ramifications. Before seeking a hearing aid4, most hearing aid users had lived with HL for more than 10 years and their impairment had progressed to moderate-to-severe levels. For many reasons, the current hearing health care (HHC) system in the United States is not meeting the needs of the vast majority of adults with HL. As the lead Federal agency promoting the Nation’s HHC, NIDCD has the responsibility, and is actively seeking, to address this problem from the public health perspective.
NIDCD Senate Report Language for FY2010 appropriations “recommends that the NIDCD support research to develop, improve, and lower the cost of hearing aids…” 5. Further, Healthy People 2020, a U.S. Department of Health and Human Services (HHS) activity that provides science-based, 10-year national objectives for promoting health and preventing disease, includes increasing the adoption rate of hearing aid usage as a HP2020 goal6. NIDCD is committed to addressing these recommendations and goals through well-developed and targeted research initiatives.
Hearing health care access
For the purposes of this working group, mild HL is defined as 26-40 dB HL averaged across 0.5 - 4.0 kHz, and moderate HL is defined as 41-60 dB HL averaged across 0.5 - 4.0 kHz. For the purposes of this working group, “hearing health care” includes assessment and access to hearing aids and non-medical treatment. “Access” includes hearing screening/assessment as well as acquiring an appropriate device and services for the individual’s hearing loss and communication needs. HHC access can be confusing to the consumer, with ill-defined professional roles and competing financial interests among provider groups. Multiple entry points include family practitioners, audiologists, hearing aid specialists, otolaryngologists, and direct Web access, as well as magazine, newspaper, and television ads.
In the U.S., in contrast to many other nations, there are no readily accessible low cost hearing screening programs, and access to low cost hearing aids exists only on the Web or through newspaper or magazine ads, all of which can be “consumer beware” situations. Hearing aids are necessary healthcare devices, and thus there is a compelling need for better alternatives for access. It is important to note that the availability of a product on the Web does not ensure that it is “accessible.” In late 2007, for individuals 65 and older, 63 percent of Americans7 and in 2009, 65 percent of British8 citizens did not use the Internet. Individuals of lower income have particularly low Internet usage rates.
Hearing health care affordability
The definition of “affordable” remains undetermined. There are likely different price points for different segments of the population. Limited scientific data are available on the specific impact of cost on hearing aid penetration/adoption rates. Yet cost is considered to be one of the primary reasons for non-adoption of hearing aids. According to the MarkeTrak VII Survey of “non-adopters,” 76 percent mentioned finances as a barrier to adoption, 64 percent said they cannot afford aids, and half indicated cost as a definite reason for not using hearing aids9.
In 2004, the average cost of one hearing aid (including the device and professional services) was approximately $1,800; 70 percent of individuals with hearing loss require two devices10. MarkeTrak VIII lists the 2008 average out-of-pocket expense for one hearing aid at $1,60011. However, this average price was computed with the inclusion of free, direct mail, and discounted aids (but not including those available through the Department of Veterans Affairs) meaning the actual cost is higher for most patients. A recent industry survey found a price range per aid between $1,182 and $2,87612. A recent consumer survey shows consumers spending $1,800 to $6,800 for a pair of hearing aids13. While the life span of a hearing aid depends on many factors, in general, hearing instruments have an average life of four to six years14. Batteries add additional costs. A hearing aid wearer, over the wearer’s lifetime, may spend tens of thousands of dollars acquiring and maintaining hearing aids. Given these factors, hearing aids can be among the most expensive items purchased by many Americans with HL, after their home or car.
Medicare does not cover the cost of hearing aids. Most insurance programs do not cover hearing aids and of those that do, most pay only a portion of the costs. In addition, approximately 46 million Americans (15 percent) are uninsured. Since government programs providing hearing aids for adults exist only for the most severely impaired, many individuals who cannot afford hearing aids rely on Lions Clubs, hearing aid loaner banks, and various other philanthropic organizations. This is not an acceptable public health solution for a necessary health care device. It is appropriate to question the assumption that the best HHC is synonymous. With the most advanced technology, especially for adults with mild to moderate hearing loss. This assumption makes HHC even less accessible for those who can least afford it.
External factors influencing accessibility and affordability
Beyond the public health urgency, four external factors influenced the need and timing of the working group: changes in the demographics and socioeconomics of the U.S. as well as new and emerging technologies and evolving service delivery paradigms.
There is a strong relationship between age and reported HL: 18 percent of adults aged 45-64, 30 percent of adults aged 65-74, and 47 percent of adults 75 years or older report HL15. America is aging, and by 2026, 30 percent of the U.S. population will be over 55 and 18 percent will be over 6516. A concomitant increase in hearing aid candidates is expected. Many will have an initial hearing loss of mild to moderate level and will be active in the workforce17.
The mission for both HHS and NIH includes closing the gaps in health disparities. NIH held an international Summit on Eliminating Health Disparities in December 2008. The Agency for Healthcare Research and Quality periodically issues a “National Healthcare Disparities Report,” with the most recent version released in 200818.
It is a public health need and mandate to address health care disparities in underserved populations. Twenty percent of Americans live in rural America; these individuals are more likely to be older, poor, in fair or poor health, and to have chronic conditions. Inner city individuals are also underserved19. Many in America have limited disposable income. Median household income (2007 Census) is $50,000. 35 percent of Americans have household income of less than $35,000. The current unemployment rate is more than 9.0 percent. Socioeconomic disparities in health care likely also exist in HHC. The estimate of Americans with underserved HHC could be higher than for health care in general because of the high cost of hearing aids and complex access to these devices. Acquiring appropriate HHC may be especially challenging for the “working poor.” It is important to remain conscious of the underserved, economically disadvantaged, and less advantaged. NIH/NIDCD research and emergent solutions should address the needs of all Americans.
Auditory assessment is being automated20. Automated hearing tests (telephone/computer/Web-based) including speech-in-noise testing are now a viable possibility 21 and in some cases are already available, as are hand-held pure-tone hearing screeners and screeners for middle ear and cochlear conditions using tympanometry and otoacoustic emissions22. Hearing aid component costs (microphone and other elements) are estimated to be less than $100, and evolving downward with technological and manufacturing advances 23. “System on a chip” technology (e.g., ASIC, Analog VLSI, DSP) offers new possibilities. Hearing aid fitting is being automated with fitting programs/algorithms routinely run on PCs. Open canal fittings offer less burdensome fitting possibilities. Research and development leading to a trainable, self-testing, and self-fitting hearing aid is ongoing24. Technological advances make it likely that audiometry, real-ear measurements, and hearing aid programming and fitting can be packaged and performed on one chip.
Changing service delivery paradigms
Beyond the traditional audiology/hearing aid specialist/otolaryngology office offering hearing aids from various manufacturers, there are now store-front hearing aid sales (e.g., Costco) as well as Internet sales, including direct-to-patient as well as Internet referral/consolidators. Telemedicine opportunities now exist for remote audiometric testing and hearing aid fitting and management25. The unbundling of costs for hearing health care services is being actively discussed (currently products and services are often combined for a single fee so the consumer is unaware of the cost for audiological services and the device). Professional workforce demographics are also changing. There is a shortage of primary care physicians. Further, if all individuals with HL sought HHC, there would be a shortage of audiologists to meet that need26. Professional organizations are now discussing the training and certification of audiology assistants and technicians (not unlike existing assistants in occupational therapy, physical therapy, and optometry) in an effort to maximize productivity of the most highly trained individuals. Convenient care clinics, providing convenient access to basic care for the most common acute conditions, are now a part of the healthcare access landscape and provide an example of new routes of access and service delivery paradigms27.
Professional issues influencing accessibility and affordability
Many interrelated issues, tensions, and conflicts across provider groups have contributed to the current HHC situation. The willingness of manufacturers to produce lower cost hearing aids and the willingness of audiologists to sell low-cost aids in the traditional distribution system is debated within and among the professions. Direct access for patients has long been a tension between professional groups (otolaryngologists and audiologists), as have the differing educational qualifications and credentialing standards of those who dispense hearing aids (audiologists and hearing specialists).
The value of current federal regulations requiring a medical evaluation has also been debated. Some support the current regulations, while others believe they add unnecessary burden and cost to the patient/consumer. The regulation (21 CFR 801.420) specifies that prospective hearing aid users should have a medical evaluation by a licensed physician, preferably an otolaryngologist, otologist, or otorhinolaryngologist. However, many of the medical clearances/evaluations that do occur are not full otologic evaluations and are conducted instead by primary care physicians. Further, many patients sign a medical waiver, essentially circumventing the medical evaluation, but exact numbers are unknown.
Working group focus
The working group specifically focused on adults with mild to moderate hearing loss. This group is least likely to have had hearing screening/assessment and is least likely to be using hearing aids due to many reasons including perceived benefit, cost, stigma, value, etc. Individuals with mild to moderate hearing loss can, however, obtain benefit from amplification strategies. Research has demonstrated that psychosocial health declines with increasing hearing loss28. Earlier hearing aid users may have better eventual outcomes with amplification, and plasticity effects may require less auditory retraining. It may be beneficial to initiate hearing health care, maintaining quality of life, before cognitive or other age-related health declines occur. In addition, many individuals with mild to moderate HL will progress to severe HL, requiring more complex professional services in later years.
The working group focus was not on identifying research needs related to the development of increasingly sophisticated or technologically complex hearing aids; nor was the focus on children or adults with severe hearing loss or complex or extensive hearing health care needs. NIDCD sought research needs that would complement and supplement, not replace, current paradigms and services. Ensuring quality was paramount in all considerations and deliberations. Research recommendations were designed to lead to outcomes increasing accessibility and affordability of hearing health care, ultimately leading to an increase in the number of hearing-impaired adults receiving quality hearing health care in the United States.
The working group was co-chaired by Dr. Amy Donahue, NIDCD/NIH; Dr. Judy R. Dubno, Medical University of South Carolina; and Dr. Lucille Beck, Department of Veterans Affairs. Twenty individuals from U.S. and international institutions, bringing varied expertise and experiences to the working group, were invited as participants. Two guest speakers from the U.S. Food and Drug Administration also participated.
Working group participants were instructed that their role was to address the pressing public health issue of accessible and affordable hearing health care and to consider the needs of all adult patients with mild to moderate HL, bringing their individual knowledge and experiences to the issue. Participants were charged not to represent the needs/agenda of the professional organizations, institutions or industries to which they belonged. Professional issues of roles and “turf” in the HHC landscape, noted above in the background section, were to be put aside. This was a necessity if the working group was to make any traction in articulating opportunities, barriers, and research needs for promoting accessible and affordable HHC for adults with mild to moderate hearing loss.
Representatives from the American Academy of Audiology (AAA), American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS), American Speech-Language-Hearing Association (ASHA), Better Hearing Institute (BHI), Convenient Care Association (CCA), Hearing Industries Association (HIA), and Hearing Loss Association of America (HLAA) attended as observers. Invited U.S. government agencies included the Agency for Healthcare Research and Quality, the Maternal and Child Health Bureau, and the Food and Drug Administration.
Agenda and working group format
To view the agenda, click here. Working group participants were provided numerous articles and other related documents to read and review prior to the meeting.
The working group convened at 3 p.m. on August 25, 2009, and began with introductory and keynote presentations. The background and purpose and charge to the working group were presented from the public health perspective by Dr. Donahue. The specific charge was to develop a research agenda leading to increased accessibility and affordability of hearing health care for adults with mild to moderate hearing loss, including accessible and low-cost hearing aids. Participants were also charged to remember the broad public health mandate and to be interactive, transparent, and collaborative.
The session then proceeded with two keynote presentations on changes in healthcare and healthcare delivery and one presentation on hearing loss, hearing aids, and quality of life.
The second day consisted of presentations and discussion related to accessible and affordable hearing screening and hearing aids. Topics included hearing healthcare bottlenecks, telehealth opportunities, rehabilitation needs, U.S. and international perspectives on hearing screening, affordable hearing aids and hearing aid delivery systems, audiology workforce needs, and medical and regulatory considerations. The second day concluded with an active discussion session among working group participants.
The third day began with additional group discussion, with the aim of articulating future research directions.
Three breakout groups were then formed to develop research questions in three general areas:
- Access (at all stages of hearing health care)
Leader: Davis, including Herer, Krumm, Mann, Weinstein, and Yueh
- Assessment (including screening)
Leader: Margolis, including Derebery, Dhar, Freeman, and Peng
- Intervention (not limited to hearing aids)
Leader: Dillon, including Cox, Dalzell, Humes, Killion, and Preves
Following group discussion, the working group reconvened as a whole, and the leader of each group presented their recommendations, during which there was additional group discussion.
This working group was intended only as the first step to addressing this important public health problem. NIDCD staff will consider these research recommendations. Future activities and initiatives seeking to address these research recommendations will be forthcoming.
The working group adjourned at 1:00 pm on August 27th.
Drs. Donahue, Dubno, and Beck subsequently compiled the recommendations for this report.
Recommendations were made in 10 areas: Access, Screening, Assessment, Innovative Hearing Aid Technology and Outcomes, Patient Variables and Outcomes, Aftercare, Delivery Systems, Workforce and Training of Hearing Health Care Providers, Medical Evaluation/Regulatory Issues and Overarching Topics. It should be emphasized that, where not noted specifically in a given recommendation, the individuals targeted throughout these recommendations are adults with mild to moderate hearing loss.
Please note: Following the working group meeting, members were asked to select recommendations considered of highest priority, in terms of both importance and immediate feasibility. The selected recommendations, which varied considerably among working group members, are noted with an asterisk below.
- *What are the barriers for patients accessing the hearing health care system, e.g., availability of services, cost, available subsidy, complexity, market forces, location, healthcare insurance coverage, and referral network?
- *What are the patient-centered factors that impact access to hearing health care, including the unique needs and concerns across the lifespan and among different cultures or special populations, e.g., perceived need, personal attitudes, stigma, socioeconomic status)?
- *What are the benefits of hearing health care to general health, economic health, lifestyle, well-being, and family?
- How do various points of access to hearing health care (e.g., self-referral, identification by screening program, direct access, referral to hearing health care professionals) affect outcomes and do these differ for different populations?
- Who comprises, and what is the size of, the unserved and underserved populations for hearing health care?
- Can new technology including social marketing be used to increase awareness of hearing, hearing loss, and access to hearing health care for young and middle-aged adult patients with mild to moderate hearing loss?
- How can access to hearing health care be improved for the “oldest old” population?
- Does early access to hearing health care change outcomes later in life?
- Does information/education about hearing loss prevention early in life increase access to hearing health care later in life or change other outcomes?
- *Develop accessible hearing screening paradigms for adults with mild to moderate hearing loss, considering both available technology and target populations.
- *Which hearing screening method (face-to-face, telephone, Internet, language-free, emerging technologies, questionnaire, audiometric, speech-in-noise) has the best sensitivity and specificity and also results in the highest rate of follow-up for individuals seeking interventions and for what populations?
- *What are the barriers to hearing screening (availability, cost, insurance policies, capitation, and financial disincentives for referral) in various health care settings (primary care offices, geriatric centers, pharmacies, convenient care clinics)?
- What variables influence and what factors promote access to hearing screening for different age and hearing loss groups?
- What is the effect of hearing screening on entry into the medical/hearing healthcare system, access to treatments (hearing aids, assistive listening devices, aural rehabilitation, medical/surgical management), and success of treatments?
- Can screening programs be developed with micro-financial incentives?
- What methods and dynamics reduce losses to follow-up (increase accessibility, reduce cost, improve education, patients’ perceived need)?
- Do special populations, such as those with co-morbid diseases/conditions, intellectual disabilities, “oldest old,” cultural or language differences, have unique screening requirements?
- What factors will influence patient awareness of and demand for hearing screening?
- What is the cost-benefit ratio for hearing screening programs for adults with mild to moderate hearing loss in various settings?
- *Are there differences in accuracy and quality between audiometry conducted in various healthcare settings and using various means of delivery (face-to-face, language-free, Internet, telephone)?
- *What assessments (e.g., auditory, cognitive, psychosocial, other) are needed to fit a hearing aid or guide other forms of intervention (as evidenced by impact on outcome)?
- Is an audiogram needed to fit a hearing aid or to determine if the patient is a candidate for other forms of intervention, such as auditory training or auditory rehabilitation? If so, does it matter how or by whom the audiometry is performed? If not, what other test methods could be used?
- Are there differences in accuracy and quality (i.e., test operating performance) between automatic and manual audiometry?
- What calibration systems are required for automatic audiometry, and for telephone and Internet screening systems?
- What factors influence patient awareness or demand for hearing assessment?
Innovative hearing aid technology and outcomes
- *What variables (technology-centered and patient-centered) predict success with amplification?
- *What is the minimal technology that will achieve success with hearing aids?
- *What is the difference in outcomes among very low cost one-size-fits-all, low cost try-and-select, individually programmed, trainable, and full-feature high-cost devices for varying patient population groups and for individual patients?
- *Develop a self-testing, self-fitting hearing aid, considering technology and patient characteristics, selection, fitting, and aftercare.
- What are the technology-centered factors (cost, appearance, and performance) that determine the penetration and utilization rate of hearing aids and how do these vary among various age, cultural, and socioeconomic groups?
- What is the effectiveness and patient satisfaction of low cost (entry level) hearing aids and full-feature hearing aids?
- What characteristics should direct-to-consumer hearing aids have to provide benefit and high-quality service?
- Can currently available lower cost hearing aids be used to increase access and reduce overall cost?
- Does trial and rejection of hearing aids cause subsequent delays in reconsidering amplification in the future?
Patient variables and outcomes
- *What factors influence a patient’s perceived need for hearing health care and motivate individuals to seek hearing health care?
- What are the characteristics of patients who would benefit from hearing aid use?
- What are the patient-centered variables (e.g., age, degree of hearing loss, socioeconomic status) that contribute to the penetration rate of hearing aids?
- How does an individual define hearing aid value (performance/satisfaction/benefit related to cost)?
- What is the relationship between degree of hearing loss (and its associated audiometric configuration) and attitudes toward hearing health care, including hearing aids?
- What factors prevent individuals who are identified by others or self-identify for hearing difficulties from acquiring hearing aids (e.g., cost, attitudes)?
- What are the concerns of patients who have purchased hearing aids but are not using them?
- What variables reinforce and/or reduce the stigma associated with hearing loss and hearing aids?
- Does early intervention improve long-term outcomes (cognitive, psychosocial, economic, general health) and are individual differences related to age and degree of hearing loss?
- Develop and evaluate an expanded IOI-HA, so that higher sensitivity can be achieved with manageable subject numbers.
- *What follow-up information and patient education components provide maximum benefit to patients with direct-to-consumer hearing aids?
- What aftercare is required for various service delivery models and what is the effect on hearing aid success?
- What are the barriers to follow-up care for users of hearing aids?
- What are the characteristics of people who benefit from auditory training in various settings and what is the role of motivation?
- What is the impact of the hearing aid orientation to long-term hearing aid success?
- Do currently available rehabilitation methods improve long-term success with hearing aids?
- *What are the opportunities to use new health care delivery models and methodologies, including telehealth, for hearing health care?
- How can current delivery systems (including the system and the provider) be utilized or modified to increase accessibility and affordability of hearing health care?
- What is the comparative effectiveness between two delivery schemes (current best practice vs. others), with technology held constant?
- What is the effect of patient-centered variables (age, cognitive ability, familiarity with technology) on willingness to access various delivery systems?
- What is the influence of the service delivery model on willingness to seek help by patients who report communication difficulties, and on patient outcomes?
- What is the minimal hearing health care delivery system needed for successful outcomes and quality care?
- Is continuity of care an important variable for hearing health care?
Workforce and training of hearing health care providers
- *What are the knowledge, skills, and abilities of hearing health care professionals (audiologists and audiology assistants) and other persons providing hearing health care (nurses, nurse practitioners, trained volunteers, caregivers, students, physician assistants)?
- *What are the training requirements for hearing health care service delivery in non-traditional settings (e.g., convenient care clinics, pharmacies)?
- How can caregivers and family members be educated and trained to address the needs of persons with hearing impairment?
- What is the capacity and need for hearing screening and assessment services?
- What mechanisms are in place to assure that physicians and audiologists provide high quality care?
Medical evaluation/regulatory issues
- *What is the appropriate medical evaluation to rule out contra-indications for using a hearing aid?
- *Do the existing FDA requirements for medical evaluation and clearance prior to hearing aid procurement provide significant protection to patients or create a significant barrier to access?
- *What percentage of hearing aid recipients opts for the medical waiver, and of these, what percentage is subsequently diagnosed with medically treatable hearing loss?
- *What is the prevalence of medically/surgically treatable causes of hearing loss in adults with mild to moderate hearing loss and in the subpopulation of those adults seeking hearing aids?
- What is the patient’s understanding of the medical evaluation/clearance and waiver?
- Can different regulatory approaches impact access without compromising hearing health care?
- What decision-making algorithms for “red flag” conditions (requiring medical consultation) are appropriate for different service delivery models (face-to-face, Internet, telephone)?
- What evidence is available that consumers are unable to identify medically treatable causes of hearing loss?
- *Develop research infrastructure supporting research on hearing health care accessibility and affordability (databases, practice networks, multidisciplinary teams).
- *Develop and evaluate a standard set of outcome measures to determine success of hearing health care and provide guidelines on how and when outcomes should be measured.
2 Collins, JG. (1997) Prevalence of selected chronic conditions: United States 1990-1992. National Center for Health Statistics. Vital Health Stat 10(194).
4 Davis, A, Smith, P, Ferguson, M, Stephens, D, and Gianopoulos, I, (2007). Acceptability, Benefit and Costs of Early Screening for Hearing Disability: A Study of Potential Screening Tests and Models. Health Technol Assess. Oct; 11(42): 1-294.
5 Senate Report 110-410, page 111, Report of the Committee on Appropriations, U.S. Senate, on S. 3230 (making appropriations to the Departments of Labor, Health and Human Services, and Education, and Related Agencies Appropriation Bill, 2009).
9 Kochkin, S. (2007). MarkeTrak VII: Obstacles to Adult Non-User Adoption of Hearing Aids. Hearing Journal. Vol. 60, No. 4: 24-50.
11 Kochkin, S. (2009). MarkeTrak VIII: 25-Year Trends in the Hearing Health Market. Hearing Review. Vol. 16, No. 11: 12-31.
12 Kirkwood, D. (2009). Despite Challenging Economic Condition, Practitioners in the Survey Remain Upbeat. Hearing Journal. Vol. 62, No. 4: 28-31.
14 http://www.maaudiology.org/faqs.asp#replace; http://www.ohio-academy-of-audiology.org/faqs.asp#replace
17 Davila, EP, Caban-Martinez, AJ, Muennig, P, Lee, DJ, Fleming, LE, Ferraro, KF, LeBlanc, WG, Lam, BL, Arheart, KL, McCollister, KE, Zheng, D, and Christ, SL, (2009). Sensory Impairment among Older U.S. Workers. Am J Public Health, 99:1378–1385. doi:10.2105/ AJPH.2008.141630
20 Margolis RH, Saly GL, Le C, Laurence J. (2007). Qualind: A method for assessing the accuracy of automated tests. J Am Acad Audiol 18, 78-89.
21 Smits C, Houtgast T (2006). Results from the Dutch speech-in-noise screening test by telephone. Ear Hear 26, 89-95
22 Davis, A, Smith, P, Ferguson, M, Stephens, D, and Gianopoulos, I, (2007). Acceptability, Benefit and Costs of Early Screening for Hearing Disability: A Study of Potential Screening Tests and Models. Health Technol Assess. Oct; 11(42): 1-294.
23 Estimated from: Davis, A, Smith, P, Ferguson, M, Stephens, D, and Gianopoulos, I, (2007). Acceptability, Benefit and Costs of Early Screening for Hearing Disability: A Study of Potential Screening Tests and Models. Health Technol Assess. Oct; 11(42): 1-294; Personal communication, Howard Weinstein, August 2009.
25 Krumm, M. (2007). Audiology telemedicine. Journal of Telemedicine and Telecare,13 (5), 224-229.
26 Margolis RH, Morgan DE (2008). Automated pure-tone audiometry: an analysis of capacity, need, and benefit. Am J Audiol 17, 109-113
27 Mehrotra, A, Liu, H, Adams, JL, Wang, MC, Lave, JR, Thygeson, NM, Solberg, LI and McGlynn, EA (2009). Comparing Costs and Quality of Care at Retail Clinics with that of Other Medical Settings for 3 Common Illnesses. Annals Internal Medicine. 151: 321-328.
28 Nachtegaal, J, Smit, J, Smits, C, Bezemer, P, van Beek, J, Festen, J, and Kramer, S. (2009). The Association between Hearing Status and Psychosocial Health Before the Age of 70 Years: Results From an Internet-Based National Survey on Hearing. Ear & Hearing, Vol. 30, No. 3, 302–312.