By Harvey Abrams
This post appeared at Hearing Views exactly five years ago (March 7, 2012). It bears another visit as a refresher course to remind audiologists of our tools of the trade and the intent of their applications. The timing of the refresher course is especially apropos as we near the end of the “lull” mentioned by Dr Abrams last week in Hearing Economics, where he called for audiologists to use “income and outcome” measures as a means of differentiating and separating our services in the commoditized hearing aid market.
The lull is a good time to brush up. It’s likely the quiet before the storm, what with the upcoming FTC Workshop on Hearing Health Technology on March 18, followed by Audiology Now! 2017, and in the midst of fascinating new research on hearing aids dispensed by different means.
In a recent MarkeTrak report, Kochkin and colleagues (2010) provide compelling evidence suggesting that our patients’ level of real-world success is directly related to the extent to which their hearing care provider follows a best-practice protocol for the selection and fitting of hearing aids.
This protocol has been detailed in clinical practice guideline documents (e.g., American Academy of Audiology; AAA, 2006) and is currently taught in most AuD training programs. Two key elements of these guidelines are verification and validation. However, there appears to be some confusion among clinicians as to how these two are distinguished from one another. To state it simply, verification is a device-centric process whereas validation is patient-centric.
THE VERIFICATION PROCESS
Verification is the process by which we determine the extent to which the device meets a set of measurable specifications or expectations. This process may include measuring the response of the hearing aid in a test chamber (the coupler response) to make sure (verify) that the hearing aid that we received from the manufacturer and the specification sheet that accompanied that hearing aid are reasonably well matched. It’s important to verify that what we received is what was sent. We might think of this process as a quality control measure.
The probe-tube measurement battery is the other verification process in a best-practices protocol. Here, we’re checking (verifying) the extent to which the hearing aid is meeting a set of pre-determined gain or output levels (targets) as measured in the ear canal. We know that the same signal in different ears (or different hearing aids in the same ear) can have dramatically different frequency/gain characteristics (and will almost certainly differ from the coupler response), so we need to measure the hearing aid response in real time in the actual ear to get an accurate measure of the hearing instrument’s gain and output characteristics.
We should also remember that there is more to the “real-ear” verification procedure than simple target matching. We also want to verify that the output of the hearing doesn’t exceed our patient’s discomfort level; that compression is occurring at the level set in the software; that the directional performance is what we expect; that the feedback-cancellation algorithm is effective; and that noise reduction is functioning properly.
Not all measures need to be conducted in the ear to verify the response, however. Pediatric audiologists are familiar with the technique of fitting the hearing aid in the coupler after measuring the difference between the coupler’s response and the child’s ear canal response (the real-ear-to-coupler difference or RECD). Only one measure (the real-ear unaided response) needs to be made in the ear; all the other verification measures can be made in the test chamber, much to the relief of both the child and the audiologist.
But what if my fitting software displays a close match between the real-ear target and the hearing aid response? Does this mean that I’ve verified the fitting?
No, it doesn’t. You may have verified the quality of the software, but not necessarily the fitting. The aided targets displayed in the fitting software are based on an average ear canal response and a predicted hearing aid response based on style, venting, and canal length characteristics. To the extent that the patient’s ear canal deviates from the average and the hearing aid characteristics deviate from what is predicted, the hearing aid may over- or under-amplify at one or more key frequencies, resulting in inadequate audibility, compromised quality, or uncomfortable loudness.
THE VALIDATION PROCESS
But what if I successfully verify my hearing aid’s performance in the coupler and in the ear? Can I be assured that my fitting will be successful?
I’m afraid not–and this is where validation comes in. Recall that validation is patient-centric. It is the process by which we measure the extent to which the treatment goals have been achieved–as perceived by the patient.
Fortunately, we have many validation tools available to us, although they don’t all measure the same thing. I tend to classify measures such as the Hearing Handicap for the Elderly (HHIE; Ventry and Weinstein, 1982) and the Abbreviated Profile of Hearing Aid Benefit (APHAB; Cox and Alexander, 1995) as indirect validation measures. While these questionnaires certainly measure benefit as perceived by the patient, we don’t know how much importance the patient assigns to the situations described in the questionnaires.
Direct validation measures, such as the Client Oriented Scale of Improvement (COSI; Dillon, James, and Ginis, 1997) or Glasgow Hearing Aid Benefit Profile (GHABP; Gatehouse, 1999) are designed in such a way as to facilitate the identification of those communication situations that cause patients their greatest frustration and those that they most want to resolve. By measuring the extent to which those “most critical” situations are perceived by our patient as being resolved following treatment, we validate the relative success of our intervention. That intervention, of course, may (and often should) include more than just amplification. By establishing treatment goals up front, we can identify the need for such interventions as assistive technology, auditory training, and group hearing rehabilitation.
What about measuring aided speech recognition in quiet and in noise? Are those considered validation methods? While we are measuring patient-specific benefit, we don’t know the extent to which, for example, a 15% improvement in speech recognition in quiet or a 2-dB improvement on the Hearing in Noise Test (HINT; Nilsson, Soli, & Sullivan, 1994) performed in the clinic will resolve our patient’s real-world communication difficulties. Consequently, we really can’t consider these in-clinic performance measures as validating the success of our treatment.
VERIFICATION AND VALIDATION ARE BOTH ESSENTIAL
In summary, verification and validation are associated with different aspects of a best-practices hearing aid selection and fitting protocol, but each is essential to ensure a successful treatment outcome.
Harvey Abrams, PhD, is the Director of Audiology Research at Starkey Laboratories. Previously, Dr. Abrams served in clinical, research, and administrative capacities with the Department of Veterans Affairs and the Department of Defense. He also teaches distance-learning courses for the University of South Florida and University of Florida. He received his master’s and doctoral degrees at the University of Florida. His research has focused on treatment efficacy and improved quality of life associated with audiologic intervention. He has authored and co-authored several recent papers and book chapters and frequently lectures on outcome measures, health-related quality of life, and evidence-based audiologic practice.
- American Academy of Audiology (2006): Guidelines for the audiological management of adult hearing impairment. Audiol Today 18:32-36.
- Cox R, Alexander G (1995): The Abbreviated Profile of Hearing Aid Benefit. Ear Hear 16:176-186.
- Dillon H, James A, Ginis J (1997): Client Oriented Scale of Improvement (COSI) and its relationship to several other measures of benefit and satisfaction provided by hearing aids. JAAA 8:27-43.
- Gatehouse S (1999): Glasgow Hearing Benefit Profile: Derivation and validation of a client-centered outcome measure for hearing aid services. JAAA 10:80-103.
- Kochkin S, Beck DL, Christensen LA, et al. (2010): MarkeTrak VIII: The impact of the hearing healthcare professional on hearing aid user success. Hear Rev 17:12-34.
- Nilson M, Soli S, Sullivan J (1994): Development of the Hearing in Noise Test for the measurement of speech reception thresholds in quiet and in noise. J Acoust Soc Am 95:1085-1099.
- Ventry I, Weinstein B (1982): The Hearing Handicap Inventory for the Elderly: A new tool. Ear Hear 3:128-134.