Reliability of real ear insertion gain in behind-the-ear hearing aids with different coupling systems to the ear canal.

0.62 MB·English

by  Jespersen, Charlotte Thunberg

International Journal of Audiology 2013; 52: 169–176
Original Article
Reliability of real ear insertion gain in behind-the-ear hearing aids
with different coupling systems to the ear canal
Charlotte Thunberg Jespersen & Kimi Nina M ø ller
GN ReSound A/S, Lautrupbjerg 7, 2750 Ballerup, Denmark
Abstract
Objective: The last decade has offered a multitude of instant fi t coupling systems to be fi tted with behind-the-ear (BTE) hearing aids. The impact of these designs on the reliability of
real ear measurements (REMs) has not been reported. The purpose of this study was to obtain REM reliability data for instant fi t coupling systems. Design: REM reliability data was
obtained for four different instant-fi t coupling systems and for standard size 13 tubing and custom earmolds. REMs were performed for all fi ve coupling systems two times and by two
examiners. S tudy sample: Ten normal-hearing individuals (20 ears) served as participants. R esults: The REM test-retest reliability is high for the four instant fi t coupling systems as
well as for the custom earmolds. The REM inter-examiner reliability is high for three of the four instant fi t coupling systems. Conclusions: Carrying out REMs with instant fi t coupling
systems appears to be fundamentally no different than performing REMs with conventional hearing aids. For either, care should be taken in probe tube placement in terms of insertion
depth and maintaining the probe tube placement, and other best practices regarding test environment and test setup should be observed.
Key Words: Real ear measurements; reliability; instant fi t coupling systems
Real ear measurements (REMs) provide clinicians with a valid and anticipated that the reliability of REMs with these instant fi t coupling
reliable way of verifying hearing-aid gain and output in situ. They systems is less as compared to the REM reliability with a standard
are the only means by which the actual hearing aid and coupling size 13 tubing and a custom made earmold. The reasoning for this
system’ s gain or output in the ear of the individual hearing-aid user is that more variability is expected in how the instant fi t coupling
can be determined. Clinical applications of REMs are many and may systems are placed in the ear canal relative to placement of custom
include verifi cation that prescriptive targets are met, documentation made earmolds.
of the fi tting, visual assistance in the fi ne-tuning process, counseling REM variability needs to be limited in order for the measure-
of the hearing-aid user and signifi cant others, verifi cation of sig- ments to be useful in a clinical decision-making process, and should
nal processing algorithms, and as a baseline measure from which be smaller than changes resulting from modifi cations made to the
to work should the clinician need to troubleshoot hearing-aid user hearing-aid fi tting. Numerous studies on reliability of REMs have
complaints related to sound processing features or general lack of resulted in best practice recommendations for test set-up, equipment,
benefi t. One of the most compelling reasons to verify hearing-aid and environment and procedures (Larson et al, 1977; Pedersen et al,
gain or output in situ is that benefi t has been shown to be greater if 1982; Wetzell & Harford, 1983; Ringdahl & Leijon, 1984; Hawkins
the measured gain or output in the ear canal is well matched to the & Mueller, 1986; Dirks & Kincaid, 1987; Killion & Revit, 1987;
target (Baumfi eld & Dillon, 2001). In addition, REMs are part of best Tecca, 1990; Ickes et al, 1991; Stone & Moore, 2004).
practice procedures for hearing-aid fi ttings today (British Society of Inter-examiner reliability of REMs has been found to be high and
Audiology and British Academy of Audiology guidelines, 2007; ISO independent of measurement equipment and hearing-aid type as long
12124, 2001; Cox, 2005; Valente et al, 2006). as a careful clinical procedure is followed (Hawkins, 1987; Valente
The last decade has offered a multitude of instant fi t coupling et al, 1990; Hawkins et al, 1991).
systems to be fi tted with BTE hearing aids. These instant fi t coupling Hawkins (1987) investigated the inter-examiner variability of
systems include thin tubes and receiver-in-the-ear designs combined real-ear-insertion-gain (REIG) using a BTE hearing aid combined
with different dome designs (Kiessling et al, 2005; Alworth et al, with a soft earmold. Six examiners did each fi ve measurements on
2010). The impact of these designs on the reliability of REMs has one participant ’ s ears using the Rastronics CCI-10 equipment in a
not been reported, but it is important for clinicians who fi t hearing fi tting room and used their own clinical procedure. At 1000 and 2000
aids using these instant fi t coupling systems to be aware of it. It is Hz the majority of the variability was within (cid:2) 3 to 4 dB. At 4000
Correspondence: Charlotte Thunberg Jespersen, Global Audiology, GN ReSound A/S, Lautrupbjerg 7, 2750 Ballerup, Denmark. E-mail: [email protected]
(Received 14 March 2012; accepted 22 October 2012)
ISSN 1499-2027 print/ISSN 1708-8186 online © 2013 British Society of Audiology, International Society of Audiology, and Nordic Audiological Society
DOI: 10.3109/14992027.2012.744105
170 C. T. Jespersen & K. N. Møller
tube movement between the unaided and aided measurements, and
Abbreviations
experience level of the examiner conducting the measurements as
BTE Behind-the-ear potential reasons for the low reliability in the study conducted by
IEC International Electrotechnical Commission Humes et al (1988). A mean test-retest reliability of 2.0 dB standard
ITC In-the-canal deviation seems to be the short-term test-retest reliability reported in
ITE In-the-ear most studies independent of hearing-aid style, measurement equip-
REAR Real-ear-aided-response ment, and environment as long as a careful clinical procedure is
REIG Real-ear-insertion-gain followed. A mean long-term test-retest reliability of 3.3 dB standard
REM(s) Real ear measurement(s) deviation has been reported by Tecca et al (1987).
REUR Real-ear-unaided-response Tecca (1990) suggested the following clinical application of REM
RITA Receiver-in-the-aid test-retest reliability. For immediate REM test-retest reliability, mea-
RITE Receiver-in-the-ear surement differences up to 2 dB can be considered measurement vari-
SPL Sound pressure level ability and only differences in excess of 2 dB should be considered
‘ real ’ differences in the amplifi cation. A clinical example of imme-
diate test-retest measurements can be a clinician wanting to verify
changes in hearing-aid settings without removing the device from the
and 6000 Hz the variability increased, half of the REIG at 6000 Hz ear. For short-term test-retest variability, measurement differences in
showed differences of more than 5 dB and 25% were greater than 10 excess of 3 – 5 dB are suggested to be considered signifi cant in clini-
dB. The author reported differences in the procedure, e.g. insertion cal settings. A clinical example of short-term test-retest measure-
depth of the probe tube, to be the reason for the low reliability in ments can be verifi cation that less low frequency gain or output has
the high frequencies. Valente et al (1990) determined inter-examiner been achieved by modifying the vent in the hearing aid or earmold.
variability of REIG in in-the-canal (ITC) and in-the-ear (ITE) hear- For long-term variability, measurement differences in excess of 6 to
ing aids. Two examiners jointly conducted measurements on either 7 dB are considered clinically signifi cant for clinicians. A clinician
right or left ear of 28 participants, using the Frye 6500 unit and might want to do a long-term measurement comparison when the
a careful procedure under anechoic conditions. The inter-examiner hearing-aid user complains of lack of benefi t after having used the
variability was insignifi cant and not reported. Hawkins et al (1991) hearing aids for a longer period.
investigated inter-examiner variability of real-ear-unaided-response The purpose of this study was to obtain REM reliability data for
(REUR), real-ear-aided-response (REAR), and REIG with a BTE instant fi t hearing-aid coupling systems, and to compare these with
hearing aid coupled to the ear with a Comply earmold. Measure- measurement reliability using hearing aids fi t with standard size
ments were conducted twice by each of the two examiners on 13 tubing and custom earmolds and following recommended clinical
24 participants using the Rastronics CCI-10 and a careful clinical procedures. Specifi cally, three measures of reliability were examined:
procedure under anechoic conditions. Inter-examiner variation was (1) reliability with the different coupling systems, (2) long-term test-
not reported specifi cally (combined with test-retest variation), but retest reliability, and (3) inter-examiner reliability.
the reliability was reported to be high.
Test-retest reliability is also of importance, and is anticipated to be Method
the largest source of variance when using instant fi t coupling systems.
Tecca (1990) refers to three different types of test-retest reliability: Subjects
the immediate-, the short-term- and the long-term test-retest reli- This study was carried out with a group of ten normal-hearing indi-
ability. Immediate test-retest variability refers to differences found viduals (20 ears). Five individuals were male and fi ve were female.
between measures completed consecutively within the same session The inclusion criteria for the participants was normal outer- and
and without removal of the earmold or hearing aid. Short-term test- middle-ear conditions with a tympanic pressure within (cid:2) 50 daPa,
retest variability refers to differences between measures conducted a tympanic compliance between 0.3 and 1.6 mmho, and a tympanic
sequentially within the same session, but where the hearing aid or volume between 0.6 and 2.0 ml. Tympanometry was done using a
earmold and probe tube is removed and reinserted for subsequent GN Otometrics Otofl ex 100. Participants were not compensated for
measurements. Long-term test-retest variability refers to differences their participation.
found between measures completed during two different sessions.
Multiple studies have been conducted on test-retest reliability
of REIG. As can be seen in Table 1, studies have been conducted Hearing aids and coupling systems
using different hearing-aid styles, different measurement equipment, Three pairs of a commercially available receiver-in-the-aid (RITA)
and different measurement environments. The majority of studies hearing aid (ReSound Live 71D devices), and two pairs of a receiver-
have investigated the short-term test-retest reliability, but Tecca et al in-the-ear (RITE) hearing aid (ReSound Live 70D RIE devices) were
(1987) have also investigated the long-term test-retest reliability of used for the REMs. All fi ve pairs of hearing aids were fi tted to amplify
REIG. the IEC ’ s standard moderate audiogram # 3 (Bisgaard et al, 2010).
The short-term test-retest reliability of REIG conducted with ITC, The hearing aids were fi tted using the Aventa 2.9.15.1 fi tting
ITE, and BTE hearing aids with conventional coupling systems has software. Amplifi cation was prescribed according to the manufac-
been shown to be high, but to decrease with frequency. The lowest turer ’ s proprietary fi tting rule, Audiogram (cid:3) , with the “ experienced
test-retest reliability is reported by Hawkins (1987) and Humes et al non-linear ” profi le selected. The Audiogram(cid:3) fi tting rule prescribes
(1988). Hawkins (1987) reports differences in the procedure, such insertion gain for narrowband signals at input levels of 50 and 80 dB
as insertion depth of the probe tube, to be the reason for the low SPL, so in this study the maximum real ear output has not exceeded
reliability. Valente et al (1990) mention a greater loudspeaker-to- 92 dB SPL at the eardrum level and can for this reason be considered
test participant distance, the possible lack of precautions to control acceptable for the normal-hearing participants. The hearing aids
Reliability of real ear insertion gain 171
e z z
g H H z z z z z z
y ran 000 000 00 H 00 H 00 H 00 H 00 H 00 H
c 6 5 0 0 0 0 0 0
equen 00 to 00 to 0 to 4 0 to 6 0 to 4 0 to 4 0 to 4 0 to 4
Fr 10 10 50 20 25 20 25 20
Confi dence 5% confi dence (cid:2)intervals of 3 dB (cid:2)to 6 dB (mean 95% confi dence interval: 3.8 dB)5% confi dence (cid:2)interval of 2 dB (cid:2)to 11.8 dB (mean 95% confi dence interval: 6.7 dB)5% confi dence (cid:2)interval of 2.0 to (cid:2) 6.9 dB (mean 95% confi dence interval: 3.3 dB)5% confi dence (cid:2)interval of 4.1 dB (mean 95% confi dence interval: 3.3 dB)5% confi dence (cid:2)interval of 2 dB (cid:2)to 4.0 dB (mean 95% confi dence interval: 3.9 dB)5% confi dence (cid:2)interval of 2.8 dB (cid:2)to 5.3 dB (mean 95% confi dence interval: 3.9 dB)5% confi dence (cid:2)interval of 5 dB (cid:2)to 12.0 dB (mean 95% confi dence interval: 6.4 dB)
9 9 9 9 9 9 9
Test-retest differences Standard deviation ranging from 2.2 to 7.0 dBStandard deviation below 2.5 dB (mean standard deviation: 1.9 dB) Standard deviation ranging from 1.0 to 6.0 dB (mean standard deviation: 3.5 dB)Standard deviation of less than 3.5 dB (mean standard deviation: 1.7 dB) Standard deviations of less than 2.1 dB (mean standard deviation: 1.7 dB) Standard deviation ranging from 0.6 to 4.0 dB (mean standard deviation: 2.0 dB)Standard deviations ranging from 1.5 to 2.7 dB (mean standard deviation: 2.0 dB)Standard deviations ranging from 1.4 to 6.0 dB (mean standard deviation: 3.3 dB)
Conditions (cid:4)AC Anechoic conditions, (cid:4)R Fitting room FR AC AC AC AC AC FR AC
F
n the literature. Measurement system Rastronics CCI-10 Rastronics CCI-10 Frye 6500 real ear analyzer Frye 6500 real ear analyzer Frye 6500 real ear analyzer Starkey RE4 interfaced with the Fonix 5500Z hearing aid analyzer Rastronics CCI-10 Starkey RE4 interfaced with the Fonix 5500Z hearing aid analyzer
d i
e
bility of REIG results report Hearing aids BTE coupled to a soft earmold BTE hearing aid coupled to the ear with a comply earmold BTE hearing aid combined with a foam earplug BTE hearing aid combined with a foam earplug ITC and ITE hearing aids BTE hearing aid combined with an individually fi tted and fully occluding earmold BTE hearing aid coupled to custom made earmold BTE hearing aid combined with an individually fi tted and fully occluding earmold
a
eli 7)
r 8
view of test-retest Study Hawkins (1987) Hawkins et al (1991) Humes et al (1988) Killion and Revit (19 Valente et al (1990) Tecca et al (1987) Purdy et al (1989) Tecca et al (1987)
er
v
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ble 1. ort–term ng-term
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172 C. T. Jespersen & K. N. Møller
were fi tted with an omnidirectional program with all features but less from the tympanic membrane was ensured in order to measure
the digital feedback suppression deactivated. The digital feedback at the level of the tympanic membrane and to avoid standing waves
suppression feature was calibrated and thereby activated in order affecting the measured SPL in the ear canal. Correct insertion depth
to be able to do the measurements without feedback squeal. Digital was ensured by a dual approach. Initially, a visual positioning, using
feedback suppression is a pure feedback cancelling feature and no a marker length of 28 mm from the end of the probe tube for females
gain reduction was applied in any of the fi ttings. and 30 mm from the end of the tube for males was used, and it was
The hearing-aid pairs were fi tted with different coupling systems. measured that the length of the probe tube from the marker to the
The different coupling systems were a pair of RITA instruments and tip of the probe tube ensured that the tip of the probe tube extended
thin tubes combined with open domes (hereafter named RITA instru- 5 mm past the sound outlet of the domes and earmolds. The marker
ments with open domes), a pair of RITA instruments and thin tubes was placed at the tragus once the probe tube was inserted. Secondly,
combined with tulip domes (RITA instruments with tulip domes), a an acoustic positioning check at 6000 Hz was done for the REUR,
pair of RITE instruments combined with open domes (RITE instru- checking that the unaided gain was not below (cid:5) 5 dB. If the unaided
ments with open domes), a pair of RITE instruments combined with gain at 6000 Hz was below (cid:5) 5 dB, the probe tube length was
double domes (RITE instruments with double domes), and a pair of adjusted and/or the probe tube was repositioned and the measure-
RITA instruments and standard size 13 tubes combined with closed ment repeated until an acceptable measurement was obtained.
custom earmolds (RITA instruments with custom earmolds). Note The measurement method used was the modifi ed pressure method
that the terminology used to describe the different types of domes in with stored equalization, as the hearing aids were fi tted with a digital
this paper is consistent with that used by the manufacturer of the test feedback suppression feature and as most of the coupling systems
hearing aids. The terms used to describe such domes differ among were open (Larsby & Arlinger, 1988; Hawkins & Mueller, 1992;
manufacturers. The thin tubes, receivers-in-the-ears, and domes were Lantz et al, 2007). A concern with the modifi ed pressure method
all of the appropriate sizes for the individual participants ’ ears. with stored equalization is that movement of the participant ’ s head
can lead to changes in the sound fi eld and thus to errors in REIG
(Shaw, 2010). Aazh et al (2012) have shown that the modifi ed pres-
Procedures sure method with stored equalization can be used if the participants
REMs were performed for all fi ve hearing aid and coupling systems can keep their head still during the measurements.
two times by two examiners. The two examiners were experienced The REUR was measured using a 65 dB SPL warble tone sweep
in making REMs and knowledgeable concerning factors affecting stimulus. Although use of this signal is not representative of cur-
reliability. The measurement order of the fi ve different coupling rent clinical practice, this choice may have reduced variability due
methods as well as the order of the examiners doing the measure- to small differences in the signal level or spectrum between mea-
ments was randomized. There was a median of one day (1st and 3rd surements or sessions. For broadband signals, the measurement
quartile of one and six days) between the test-retest measurements. equipment adjusts the overall presentation level based on the level
Test room conditions, equipment, and participant orientation in at the reference microphone but does not ensure that the desired
the test room, probe tube calibration, and probe tube placement were signal spectrum is obtained. When a narrowband signal is used, the
consistent with the British Society of Audiology and British Acad- level of each frequency presented is controlled. Then the coupling
emy of Audiology guidelines (2007). REMs were obtained in a quiet system and hearing aid was carefully inserted into the ear. The real-
fi tting room complying with the ISO 12124 (2001) standard and ear-occluded-response was measured with the hearing aid turned off
using an Aurical Plus from GN Otometrics that had been calibrated and with a warble tone sweep stimulus and it was checked that the
within the last 12 months prior to the measurements. The Aurical gain/output was not reduced much in the low frequencies, if this
Plus complies with the IEC 61669 (2001) standard. was the case then the hearing aid was repositioned and the probe
The loudspeaker was positioned with no large refl ecting surfaces tube was checked for wax/moisture. The hearing aid was turned on
near the participant. The loudspeaker and the reference microphone and the REAR was measured. The measurements were conducted
when positioned on the participant were both one meter away from at 129 frequencies from 200 Hz to 8000 Hz. REIG was calculated
the nearest refl ective surface. by the measurement equipment, and this data was used for analysis.
Probe tube calibration was performed with beveled end probe Data were electronically exported from the Aurical Plus software to
tubes and by placing the probe tube so that it was close to the ref- a spreadsheet for analysis.
erence microphone aperture, without blocking either of the micro-
phones. Probe tube calibration was done with the headset placed
Results
on the ears of the participant, who was seated 0.5 meters in front
of the loudspeaker with the microphone and probe tube facing the The long-term REM test-retest and inter-examiner reliability of
loudspeaker at an angle of 0° azimuth. A probe tube calibration using the different instant fi t coupling systems was compared with the
a 65 dB SPL warble tone sweep stimulus was obtained every time measurement reliability using RITA hearing aids fi t with custom
a new probe tube was used, and was as a minimum done for each earmolds.
participant. A multivariate analysis of variance (MANOVA) was used to assess
For REMs, the participants were seated in a chair at a distance of the effect of factors and interactions on several response variables
0.5 meters facing (0 degrees azimuth) the loudspeaker and at a level (129 frequencies). Three fi xed factors were investigated: type of
with the center of the loudspeaker itself. The participants were told to coupling systems (X1), examiner (X2) and number of measurements
visually fi xate on a location on the loudspeaker during all measure- performed by the same examiner (X4). Participants are a random
ments, but their head was not held stationary. The participants were effect (X3). Two-way interactions between the fi xed effects were
asked to sit quietly during the measurements. included in the MANOVA. The mean response across right and left
Correct insertion depth with the probe tube extending at least ear was analysed in the MANOVA. Multivariate normality was veri-
5 mm beyond the tip of the domes and earmolds and being 6 mm or fi ed with the help of a Q-Q plot of the standardized residuals against
Reliability of real ear insertion gain 173
Table 2. MANOVA table. Columns denote the sources of variation (Coupling system (cid:4) X1,
Examiner (cid:4) X2, Participants (cid:4) X3, Number of measurement performed by the same examiner (cid:4) X4),
degrees of freedom (DF), Pillai, approx F, num Df, den Df and the probability of observing the F statistics
under the null hypothesis (Pr ((cid:6) F).
Source DF Pillai Approx F num Df den Df Pr((cid:6) F)
X1: Coupling system 4 3.5631 3.1614 516 200 (cid:7) 2.2e-16
X2: Examiner 1 0.8358 1.8549 129 47 0.008455
X3: Participants 9 8.0484 3.6059 1161 495 (cid:7) 2.2e-16
X4: Number of measurement 1 0.7106 0.8945 129 47 0.692476
performed by same examiner
X1 * X2 4 2.7584 0.8611 516 200 0.903060
X1 * X4 4 2.6384 0.7511 516 200 0.993685
X2 * X4 1 0.8339 1.8295 129 47 0.009710
Residuals 175
The “ * ” denotes interaction between factors.
their expected values under normality. The assumption holds. magnitude of the detected differences is negligible, therefore even
There were ten participants (20 ears) in each “ C oupling system though signifi cant differences were detected, they have no clinical
* Examiner * Participants * Number of measurement performed interest.
by the same examiner ” combination. The “* ” denotes interaction To limit the risk of false positive results, a Bonferroni correction
between factors. The results are summarized in Table 2. Whenever was applied. Only signifi cant coupling system differences at the cor-
signifi cant and meaningful effects were found, a Bonferroni correc- rected Bonferroni signifi cance level were found.
tion was used to locate differences. The mean absolute long-term test-retest differences across fre-
The approximate F statistics show signifi cant differences on two quencies with standard deviations for test-retest differences are
of the four independent factors. The measured REIG values differ shown for all four instant fi t coupling systems compared to the mean
signifi cantly with different coupling systems (F (cid:4) 3.16, p (cid:7) 0.0001). absolute long-term test-retest differences with standard deviations
The measured REIG values obtained by different examiners differ for test-retest differences for the custom earmolds across frequen-
signifi cantly (F (cid:4) 1.85, p (cid:4) 0.0084). The measured REIG values do cies in Table 3. The measurements for the two examiners have been
not differ signifi cantly between the different measurements done by combined. The table illustrates intra-frequency differences for the
the same examiner (F (cid:4) 0.89, p (cid:4) 0.6924). different coupling systems.
The interaction between the coupling system and examiner The mean absolute inter-examiner differences across frequencies
(X1 * X2) is not signifi cant (F (cid:4) 0.86, p (cid:4) 0.9030), indicating that the with standard deviations for inter-examiner differences are shown
differences between the coupling systems are not due to differences for all four instant fi t coupling systems and for the custom earmolds
between the measurements done by the two examiners. The interac- across frequencies in Table 4. The fi rst and second measurements
tion between coupling system and number of measurement done by for the two examiners have been combined as no signifi cant test-
the same examiner (X1* X4) is not signifi cant (F (cid:4) 0.75, p (cid:4) 0.9936), retest differences were found with any of the coupling systems. The
indicating that the differences between the coupling systems are not table illustrates intra-frequency differences for the different coupling
due to differences between the different measurements done by the systems.
same examiner. The interaction between examiner and number of The mean REIG across frequencies for all four instant fi t coupling
measurement (X1* X4) is signifi cant (F (cid:4) 1.82, p (cid:4) 0.0097), but the systems compared to the mean REIG for the custom earmolds is
Table 3. Mean absolute test-retest differences in dB across frequencies with standard deviations for test-retest differences.
RITA w/earmold RITA w/tulip dome RITA w/dome RITE w/double dome RITE w/dome
Frequency (Hz) Test-retest diff SD Test-retest diff SD Test-retest diff SD Test-retest diff SD Test-retest diff SD
250 0.8 (cid:2) 0.9 0.3 (cid:2) 0.3 0.3 (cid:2) 0.2 0.3 (cid:2) 0.4 0.2 (cid:2) 0.2
500 1.4 (cid:2) 1.8 0.5 (cid:2) 0.8 0.2 (cid:2) 0.2 0.7 (cid:2) 0.9 0.3 (cid:2) 0.2
750 1.6 (cid:2) 2.1 1.7 (cid:2) 1.9 0.5 (cid:2) 0.4 1.4 (cid:2) 1.5 1.0 (cid:2) 0.9
1000 1.3 (cid:2) 1.7 2.0 (cid:2) 2.2 0.8 (cid:2) 0.6 1.8 (cid:2) 1.6 1.3 (cid:2) 1.1
1500 1.0 (cid:2) 1.1 1.8 (cid:2) 1.4 1.1 (cid:2) 1.0 1.4 (cid:2) 1.3 1.7 (cid:2) 1.4
2000 1.3 (cid:2) 1.1 1.8 (cid:2) 1.3 1.1 (cid:2) 1.1 1.3 (cid:2) 1.3 1.6 (cid:2) 1.3
3000 1.3 (cid:2) 0.9 1.8 (cid:2) 1.4 1.1 (cid:2) 1.1 1.0 (cid:2) 0.8 1.1 (cid:2) 0.9
4000 1.1 (cid:2) 1.0 1.8 (cid:2) 1.5 1.2 (cid:2) 1.4 1.1 (cid:2) 0.8 1.2 (cid:2) 0.8
5000 1.7 (cid:2) 1.2 2.2 (cid:2) 1.8 1.5 (cid:2) 1.5 1.8 (cid:2) 1.3 1.4 (cid:2) 1.2
6000 1.9 (cid:2) 1.5 2.4 (cid:2) 1.9 2.3 (cid:2) 2.1 2.2 (cid:2) 1.6 2.3 (cid:2) 1.7
8000 3.4 (cid:2) 2.7 3.9 (cid:2) 2.7 3.2 (cid:2) 2.8 3.9 (cid:2) 2.9 2.5 (cid:2) 1.8
174 C. T. Jespersen & K. N. Møller
Table 4. Mean absolute inter-examiner differences in dB across frequencies with standard deviations for inter-examiner differences.
RITA w/earmold RITA w/ tulip dome RITA w/ dome RITE w/ double dome RITE w/ dome
Frequency (Hz) Inter-examiner diff SD Inter-examiner diff SD Inter-examiner diff SD Inter-examiner diff SD Inter-examiner diff SD
250 0.0 (cid:2) 0.1 0.1 (cid:2) 0.1 0.0 (cid:2) 0.0 0.1 (cid:2) 0.2 0.0 (cid:2) 0.0
500 0.3 (cid:2) 0.6 0.1 (cid:2) 0.6 0.1 (cid:2) 0.1 1.2 (cid:2) 1.4 0.1 (cid:2) 0.2
750 0.1 (cid:2) 0.4 0.6 (cid:2) 0.9 0.0 (cid:2) 0.1 2.4 (cid:2) 1.5 0.3 (cid:2) 0.1
1000 0.2 (cid:2) 0.2 0.9 (cid:2) 1.1 0.1 (cid:2) 0.2 2.4 (cid:2) 0.8 0.5 (cid:2) 0.2
1500 0.1 (cid:2) 0.2 0.6 (cid:2) 0.7 0.1 (cid:2) 0.1 0.4 (cid:2) 0.3 0.5 (cid:2) 0.4
2000 0.2 (cid:2) 0.2 0.4 (cid:2) 0.4 0.3 (cid:2) 0.5 0.6 (cid:2) 0.2 0.3 (cid:2) 0.5
3000 0.1 (cid:2) 0.2 0.7 (cid:2) 0.0 1.0 (cid:2) 0.1 0.3 (cid:2) 0.4 0.0 (cid:2) 0.3
4000 0.1 (cid:2) 0.1 0.9 (cid:2) 0.0 1.3 (cid:2) 0.3 0.3 (cid:2) 0.3 0.0 (cid:2) 0.2
5000 0.1 (cid:2) 0.1 1.5 (cid:2) 0.4 2.0 (cid:2) 0.5 0.1 (cid:2) 0.2 0.2 (cid:2) 0.1
6000 0.0 (cid:2) 0.1 1.1 (cid:2) 0.7 2.1 (cid:2) 1.0 1.0 (cid:2) 0.1 1.5 (cid:2) 0.1
8000 0.6 (cid:2) 1.0 0.7 (cid:2) 0.7 0.0 (cid:2) 1.3 0.5 (cid:2) 2.0 1.4 (cid:2) 0.4
shown in Table 5. The mean has been calculated based on all four reliability, which have documented high test-retest reliability with
measurements. different types of hearing aids when a careful clinical procedure
was followed (Ringdahl & Leijon, 1984; Hawkins, 1987; Tecca et al,
Discussion 1987; Killion & Revit, 1987; Valente et al, 1990; Hawkins et al,
1991). The data from the present study shows that high long-term test-
It was hypothesized that greater variability in how instant fi t coupling
retest reliability also applies to REMs conducted on RITA and RITE
systems can be placed in the ear canal relative to BTE fi t with standard
instruments with different instant fi t coupling systems.
tubing and custom earmolds would result in lower reliability of REMs.
The standard deviations for long-term test-retest differences are
This was mostly not supported by the current study. Except for small
all at or below (cid:2) 2.9 dB in this study and thereby smaller than the
differences in one condition which are judged to have neglible clinical
long-term standard deviations in the study by Tecca et al (1987). As
relevance, reliability was found to be equivalent across measurement
clinically signifi cant differences are often considered to be 2 SD,
conditions, between tests, and between the two examiners. In addition,
this means that measurement differences in excess of (cid:2) 6 dB can
reliability was as high or higher than that reported in the literature.
be considered clinically signifi cant.
The long-term test-retest reliability is high for the four differ-
The test-retest reliability in this study was determined by one
ent instant fi t coupling systems as well as for the custom earmold
test measurement and one retest measurement (two REIG measure-
coupling systems, as long as a careful clinical procedure is followed.
ments) as in the studies by Tecca et al (1987), Humes et al (1988),
This means that the measurement variability between measures com-
Purdy et al (1989), Valente et al (1990), and Hawkins et al (1991).
pleted with the same hearing aid, hearing-aid settings and in the same
More retest measurements may have been desirable as in the studies
ear but during two different sessions is small. This result supports
by Hawkins (1987) and Killion and Revit (1987), wherein four retest
that long-term test-retest reliability is high provided adherence to
measurements (fi ve REIG measurements) were conducted. However,
careful clinical procedures for probe tube placement and stability
of probe tube placement between measurements (Dirks & Kin- the test-retest reliability reported in the different studies is very close
caid, 1987; Hawkins & Mueller, 1986). This result is in agreement regardless of the number of retest measurements, with the exception
with previous studies on both short-term and long-term test-retest of Humes et al (1988) and Hawkins (1987), where lower test-retest
reliability likely was due to procedural factors. The high test-retest
reliability found in this study is for this reason considered to be valid.
Table 5. Mean REIG across frequencies for all four instant fi t coupling REM reliability across frequencies was not the objective of this study,
systems compared to the mean REIG for the custom earmolds. but in agreement with fi ndings from previous studies (Larson et al,
1977; Wetzell & Harford, 1983; Ringdahl & Leijon, 1984) data from
RITA RITA RITA RITE RITE
the present study (Table 3) shows greater variability for REMs at
w/earmold w/tulip dome w/dome w/double dome w/dome
higher frequencies. Basic physical principles determine that at higher
Frequency frequencies a larger accuracy in positioning the probe tube inside the
(Hz) REIG REIG REIG REIG REIG ear canal is needed in order to measure the correct gain. Adherence
250 2.2 0.4 0.2 (cid:5)0.2 (cid:5)0.2 to a careful clinical procedure is likely to continue to become even
500 4.5 0.8 0.2 2.3 0.8 more important as hearing aids with broader frequency ranges are
750 10.4 3.1 1.1 5.6 3.2 developed and REMs will be conducted up to higher frequencies
1000 14.5 5.4 2.5 10.9 8.5 than the 8000 Hz in this study and the 4000 and 6000 Hz in previ-
1500 10.5 6.4 4.2 15.2 14.1 ous studies.
2000 9.0 5.7 6.6 14.5 16.6 The data in Table 3 show a tendency for larger variability in the
3000 6.7 7.5 9.9 15.7 18.3 low frequencies with the RITA instruments with custom earmolds
4000 6.2 7.4 8.8 10.8 13.7 as compared to any of the instant fi t coupling conditions. The dif-
5000 7.2 10.1 11.8 9.1 10.6
ference between the RITA instruments with custom earmolds and
6000 10.2 13.8 14.9 13.5 12.5
the RITE instruments with double domes is smaller than with the
8000 3.1 8.1 9.3 13.7 10.9
other instant fi t coupling systems. This tendency is likely to be due
Reliability of real ear insertion gain 175
to greater variation in the way that the custom-made earmolds fi t in the probe tube placement, and other best practices regarding test
each ear, and the amount of slit-leakage that may have occurred for environment and test setup should be observed.
each individual. The open domes and tulip domes provide virtually
the same venting conditions in all normal adult ear canals. Therefore Acknowledgements
the response is not predominated by the electroacoustic gain but
rather by the direct sound entering the ear canal. For the double dome The authors would like to thank Jennifer Groth for providing input
coupling system, the degree of occlusion in individual ear canals to the manuscript and Tobias Piechowiak for help with the statistical
can be expected to be more variable than the open and tulip domes. analysis of the data.
This would explain why the variability in this condition is greater
than with the custom earmolds, but less than with the less occluding
Declaration of interest: Charlotte Thunberg Jespersen and Kimi
instant fi t coupling systems.
Nina M ø ller are employees of GN Resound A/S. The authors alone
High inter-examiner reliability of REMs is desirable, as it means that
are responsible for the content and writing of the paper.
REMs can be conducted by different audiologists without it affecting
the measurement result. The REM inter-examiner variability is on the
order of 1.5 dB, which can be considered a high reliability for three of References
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