Probe-Microphone Measurements

Author: Rachel Burnett and David R. Cunningham, Ph.D.

Frequency of Use and Reasons for Non-use among ADA Members
The need for probe-microphone measurements is well established, but not all audiologists are performing these measurements. In 2003, Mueller found that of clinicians who use prescriptive fitting procedures, only 44% used probe-microphone measurements to verify the fitting (Mueller, 2003). In a later survey, including only clinicians who owned or had access to the equipment, approximately 40% used probe-microphone routinely, while approximately 50% did not use it routinely (Mueller et al, 2010).

The purpose of this research was to specifically determine how many members of the Academy of Doctors of Audiology (ADA) use probe-microphone measurements. This particular subset of practicing audiologists was surveyed for two reasons:
  1. 1) The ADA was willing to supply its member database to support this research and share it with members, and
  2. 2) Members of this professional organization are likely to be actively involved in hearing aid evaluation, fitting and follow-up services. A related purpose was to compare our findings to the frequency of probe-microphone measurement use reported in previous published articles.
Figure 1. Use of probe microphone measurements by ADA members

An e-mail survey was sent to the 799 members of the Academy of Doctors of Audiology (ADA) with permission. The respondents were asked to complete the survey anonymously. This is believed to be a representative sample of the ADA membership. The response rate was 18.4% or 147 surveys. Appendix 1 is a sample of the survey questions.

Those who participated were ADA members holding Au.D. degrees (82%), master’s degrees (9%) and Ph.D. degrees (9%). The number of years in practice ranged from 0 years to 20+ years. Practice settings included ENT, non-profit, private, university setting, VA, hospitals and other. However, 80% of the respondents were in private practice. Additionally, 90% fit primarily adults. Probe-microphone measurement systems are available to 94% of the respondents, and 6% do not have access to probe-microphone systems.

Of those who had a probe-microphone measurement system available, 93.5% used probe-mic measures. However, their frequency of use varied. As seen in Figure 1, approximately 67% reported that they use probe-mic measures for every patient, 16% for difficult patients only, and 2 % only when there is adequate time to complete the measures.

For those who do not have a probe-microphone measurement system available, 87.5% said they would use it if it were available. Only 12.5% said they would still not use probe-mic measures, even if it were made available.

While these are remarkably encouraging findings, we wanted to look into those who do not use probe-mic measures. Approximately 19% of those surveyed do not use probe-mic measures routinely regardless of their availability (currently available or made available). The various reasons associated with non-use of probe-microphone systems are seen in Figure 2.
Figure 2. Reports reasons for non-use for survey participants
Response # of responses % of responses
Too time consuming 6 20%
Does not add to decision making/ does not add valuable information 3 10%
Feel unsure how to use the equipment 3 10%
The use of real-ear measurements was not emphasized during my clinic training 3 10%
I believe manufacturer's "first-fit" algorithm is sufficient 2 6.67%
Adjusting hearing aids based on patient report is sufficient 5 16.67%
There is uncertain correlation between real-ear measurements and the patients' satisfaction with the hearing aid 4 13.33%
Real-ear measurements don't work with digital hearing aids 0 0%
Other 4 13.33%
The chart shows that two most common reasons for non-use are 1) too time consuming and 2) adjusting hearing aids based on patient report is sufficient. Investigating these reasons further we find flaw in their rationale, which is worthy of additional commentary.

According to Mueller (2001), probe-microphone measures take about five extra minutes per ear. One study (Cunningham, et al., 2002) indicated that the use of verification using probe-microphone measures saved time on follow-up visits for “tweaking” the hearing aid settings and ultimately lead to improved patient satisfaction. Another report by Christensen and Groth (2008), indicated that the number one mistake that clinicians make is the failure to use probe-microphone measurements when fitting hearing aids. Additionally, Kochkin et al (2010) showed a relationship between patient outcomes and a clinician’s ability to conduct a comprehensive clinical protocol, which included the use of probe-microphone measures.

Another line of reasoning, often stated for failure to conduct probe-microphone measures to ensure that a prescriptive fitting target has been approximated, is related to immediate patient acceptance of the fitting. That is, for some audiologists immediate patient acceptance of starting point gain and output is a higher priority than ensuring audibility of lost speech sounds has been restored. Many audiologists anecdotally report that generic prescriptive fitting targets, like both the NAL and DSL family of targets provide too much gain for inexperienced hearing aid users. Therefore, these audiologists are likely to reason that probe-microphone measures are not necessary. This line of reasoning is spurious. Even if your primary objective on the day of the fitting is maximizing immediate patient acceptance of the hearing aid, probe-microphone measures can ensure that the frequency response of the hearing aid is smooth and undistorted and that special features, such as DNR, are functioning properly.

Only eight audiologists who participated in the survey did not have a probe-mic system available. Of those respondents, seven audiologists said they would use them, if they were available. However, only about half of respondents without a probe-mic system available would purchase one. The other half were not willing to purchase the equipment due to a limited budget and/or because other equipment takes priority.

One of the most thought provoking results of the survey was related to the optional comments made by respondents. Of the 147 respondents, 71 left comments about probe-mic measures. The comments were grouped into three categories: 1) those who agree with and use probe-mic measurements (positive), 2) those who think probe-mic measurements are a good idea, but do not always use them (passive), and 3) those who do not like to use them (negative). Those who left positive comments made up 71% of the responses. Approximately 17% were passive. Those who had a negative comment made up 11% of responses. Those who support or passively support the use of probe-microphone measures (categories 1 and 2) described the use of probe-mic as a standard of care, accurate, quick, easy, effective and valuable. Many included comments indicating that they believe that not using probe-mic measurements is unethical and a disservice to patients. Respondents described their own use of probe-mic measures that included counseling and troubleshooting. These respondents also added that patients ask for probe-mic measures and that these patients were pleased that the measures were conducted during their fitting appointment.

Those who do not support the use of probe-mic measures (category 3) commented that they were not a good indicator of a successful fitting, and thus found it difficult to justify their use. Many reported that even if they used them, they would adjust the fitting based on the comments of the patients. Results of this survey indicate approximately 80% of ADA members fully appreciate the scientific value of probe-microphones and their role in the prescriptive fitting method. The other 20% of ADA members are likely to rely exclusively on patient judgments throughout the fitting process and may not fully understand or appreciate the value of prescriptive fitting methods and the use of probe-mic in the verification process.

This survey suggests an exceptionally high number of ADA members utilize probe-microphone measures as part of their hearing aid fitting process. Other similar surveys indicate a far lower use rate among audiologists. This difference in probe-mic utilization rates is worth consideration. Differences in survey methodology as well as the wording of the questions might account for some of these differences.

Unlike previous studies that found that less than half of audiologists were using probe-mic measures, this survey indicates that more than two-thirds of ADA members are using probe-mic measures for every patient. While this number is dramatically high compared to previous surveys, it may be a result of the population surveyed. A previous study surveyed Audiology Online subscribers, which may include more audiologists who don’t actively fit hearing aids than the ADA population. ADA members are primarily clinicians in private practice. One could argue that this sub-category of audiologists is likely to understand the impact that quality control mechanisms, such as probe-microphone measures, can have on the profitability of their business. Therefore, they may be more likely to routinely conduct them. While this survey reported exceptionally high utilization rates for ADA members, there are threats to its validity. Those who use probe-mic measurements may be more likely to participate in the survey, and the response rate was relatively low compared to similar surveys. We cannot necessarily assume that these results will generalize to the entire ADA membership.

The purpose of this research was to determine how many members of the Academy of Doctor’s of Audiology (ADA) use probe-microphone measurements. An email survey was sent to 147 ADA members with the findings that 1) 93.5% of members surveyed use probe-microphone measurement systems in some capacity, 2) of those who do not currently use probe-microphone measurements, 87% would if the system was made available and 3) only 19% would not routinely use probe-mic measures regardless of their availability. Additional research might try to achieve a higher response rate from this group. Outcomes could include developing education and training for those who do not routinely use probe-mic measures. The vast majority of ADA members who responded to this survey are likely to believe that verifiable results are important to their patients.    
Christensen L, & Groth J. Top ten clinician mistakes in geriatric hearing aid fitting. Seminar presented at: American Academy of Audiology; April 2008; Dallas.

Cunningham, D., Laó-Dávila, R., Eisenmenger, B., & Lazich, R. (2002). Study finds use of Live Speech Mapping reduces follow-up visits and saves money. Hearing Journal, 55(2), 43.

Kochkin, S., Beck, D., Christensen, L., Compton-Conley, C., Fligor, B., Kricos, P., McSpaden, J., Mueller, G., Nilsson, M., Northern, J., Powers, T., Sweetow, R., Taylor, B., & Turner, R. (2010). MarkeTrakVIII: The Impact of the Hearing Healthcare Professional on Hearing Aid User Success. Hearing Review, 17(4), 12.

Mueller, G. (2001). Probe-mic assessment of digital hearing aids? Yes, you can! Hearing Journal, 54(1), 10-17.

Mueller, G. (2003). Fitting test protocols are more honored in the breach than the observance. Hearing Journal, 56(10), 19-20.

Mueller, G. (2005). Probe-mic measures: Hearing aid fitting’s most neglected element. Hearing Journal, 58(10), 21.

Mueller, G. & Picou, E. (2010). Survey examines popularity of real-ear probe microphone measures. Hearing Journal, 63(5), 27.

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