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In figure 4, speech perception scores are plotted against the ASM and ASV of levels. Figure 4a, c shows a
significant correlation between speech perception scores and T-level and DR (r = 0.34, p < 0.01, and r =
0.33, p < 0.01, respectively). No significant correlation of speech perception with the ASM of the M-level
was found. Figure 4d–f illustrates the absence of a significant correlation between speech perception and
ASV of the T-level, M-level or DR. These panels also show that the ASV was relatively small in most cases,
with data clustering around a value of 1 or 2 dB, meaning a relatively flat level profile. The word scores
showed a small negative correlation with duration of deafness (3% decrease in word score for a 10-year
duration of deafness; r = 0.23, p < 0.01; data not shown).
The solid lines in figure 5a show the T-values (in decibels) along the array (measured 1 year postoperatively)
for 4 quartile groups of the overall T-level. For all groups, an increase towards the basal end was found,
which was independent of the actual overall T-level. A mixed linear model based on the measured T-levels
of randomly chosen 70% of the subjects found that the best fit of this increase was given by the following
quadratic function with only electrode
2
duo
and electrode
duo
as significant parameters:
The interaction of electrode duo with the ASM of T-levels did not reach significance (p > 0.05).
To predict the T-level for each 16 separate electrodes for an individual subject, instead of the 8 electrode
duos, electrode duo from equation 1 should be substituted by (½ × electrode + ¼). Finally, the overall
level can be determined by measuring the T-level measurement of one electrode. It turned out that the best
Population-Based Prediction of Fitting
Levels
Audiol Neurotol 2015;20:1–16
DOI: 10.1159/000362779
7
ited number of cases (>1.5 × IQR). Assuming a normally
distributed data set, this means that about 1 out of 50 (the-
oretically 2.15%) has a ratio of 10% or below. Further-
more, from figure 2a, it can be seen that the ratio was
fairly stable along the array. Figure 2b shows that about
one third of the variance of the T-/M-level ratio could be
predicted by the T-level (r = 0.61, p < 0.01). On the other
hand, the T-/M-level ratio did not show any correlation
with the M-level (fig. 2c), while it had a significant nega-
tive correlation with the DR ( = –0.42, p < 0.01; fig. 2d).
The overall T-level turned out to be very weakly cor-
related with duration of deafness (approx. 4 CU per de-
cade; r = 0.22, p < 0.05) and not correlated at all with age
at implantation (p = 0.63). In contrast, the overall M-lev-
el was not significantly correlated with duration of deaf-
ness (p = 0.57), but a small but significant negative cor-
relation was ound with age at implantation (approx. 15
CU per decade; r = 0.23, p < 0.01).
The changes in T-level, M-level and DR during the
first year are shown in figure 3. Figure 3a show the levels
along the electrode array during initial fitting and after 1
year of follow-up, expressed in clinical units. Figure 3b
shows the same data, now plotted using a decibel scale.
M-levels (fig. 3a) showed a larger increase (40.6 CU; SD
83.8) than T-levels (11.0 CU; SD 24.3), resulting in an in-
crease in DR (29.8 CU; SD 73.0). T-and M-levels ex-
pressed in decibels (fig. 3b) showed an approximately
equal increase (1.8–1.7 dB; SD 3.58–2.78), resulting in a
stable DR in the first year (–0.2 dB; SD 3.2).
In figure 4, speech perception scores are plotted against
the ASM and ASV of levels. Figure 4a, c shows a signifi-
cant correlation between speech perception scores and
T-level and DR (r = 0.34, p < 0.01, and r = 0.33, p < 0.01,
respectively). No significant correlation of speech percep-
tion with the ASM f the M-l vel was found. Figure 4d–f
illustrates the absence of a significant correlation between
speech perception and ASV of the T-level, M-level or DR.
These panels also show that the ASV was relatively small
in most cases, with data clustering around a value of 1 or
2 dB, meaning a relatively flat level profile. The word
scores showed a small negative correlation with duration
of deafness (3% decrease in word score for a 10-year du-
ration of deafness; r = 0.23, p < 0.01; data not shown).
The solid lines in figure 5a show the T-values (in deci-
bels) along t r ay (measured 1 year posto eratively) for
4 quartile groups of the overall T-level. For all groups, an
increase towards the basal end was found, which was inde-
pendent of the actual overall T-level. A mixed linear model
based on the measured T-levels of randomly chosen 70% of
the subjects found that the best fit of this increase was given
15+16
T-levels
DR
M-levels
13+14
11+12
9+10
7+8
5+6
5+6
3+4
1+2
15+16
13+14
11+12
9+10
7+8
3+4
1+2
50
100
150
200
250
0
Level (CU)
Electrode duo
a
-18
-12
-6
6
0
12
Level (dB)
Electrode duo
b
logDR
Levels at 1 year
Levels at initial fitting
logM-
levels
logT-
levels
Fig. 3.
T-levels, M-levels and DRs at initial fitting and after 1 year in clinical units (
a
) and in decibels (
b
). Arrows
point from the initial fit line towards the 1-year data.
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LeidenUniversity
145.88.209.33 - 11/23/20142:34:38PM
Fig. 3.
T-levels, M-levels and DRs at initial fitting and after 1 year in clinical units (a) and in decibels (b). Arrows point from the initial
fit line towards the 1-year data.
Population-Based Prediction of Fitting
Levels
Audiol Neurotol 2015;20:1–16
DOI: 10.1159/000362779
by the following quadratic function with only electrode
2
duo
and electrode
duo
as significant parameters:
T-level
(
electrode
duo
) = 0.04 ×
electrode
2
duo
+ 0.03 ×
electrode
duo
(
in dB
).
(1)
The interaction of electrode
du
with the ASM of T-levels
did not reach significance (p > 0.05).
To predict the T-level for
for an individual subject, inst
electrode
duo
from equation
(½ × electrode + ¼). Finally,
termined by measuring the
electrode. It turned out that
mean correlation coefficient
T-level (dB)
–18
Electrode duo
1 + 2
3 + 4
5 + 6
7 + 8
9 + 10
11 + 12
13 + 14
15 + 16
–15
–12
Electrode duo
1 + 2
3 + 4
5 + 6
7 + 8
9 + 10
11 + 12
13 + 14
15 + 16
Electrode duo
1 + 2
3 + 4
5 + 6
7 + 8
9 + 10
11 + 12
13 + 14
a
1 2 3 4 5 6 7
Electrode of
r-value
0
0.20
0.40
.60
0.80
1.00
b
Fig. 5.
a
Measured and predicted T-levels fitted with a random70%
of the population. Data plo ted in quartile groups of ASM.
b
Dis-
tribution of r-values fitting with single T-level measures at differ-
ent electrodes (electrodes 2, 5, 9 and 14 not included; electrodes
active in less than 33% of the subjects).