Comparability to other hearing measures

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procedure could consist of using triplet scoring for the first triplets to reach the correct SRT range, followed by a switch to digit scoring.

The NHT and its first adaptations to different languages were developed for landline telephones (Smits, Kapteyn and Houtgast, 2004; Jansen et al., 2010; Watson et al., 2012), but landline telephone versions were quickly replaced by internet and mobile device applications (Vlaming et al., 2014;

Potgieter et al., 2016; De Sousa et al., 2018; Han et al., 2020; Ceccato et al., 2021). This improved the reliability and precision of the tests, as landline telephone networks had limited the test material bandwidth to 300–3400 Hz. Internet and mobile device applications use a broadband signal which enables better detection of high frequency hearing loss (Jansen et al., 2013).

Despite minor developmental and procedural differences, and major linguistic differences between the different language versions of the DTT, studies have reported similar, good reliability measures. For most test versions, the slopes for the intelligibility function are steep, i.e., 15–25%/dB SNR ((Jansen et al., 2010; Potgieter et al., 2016; Giguère et al., 2020). A steep intelligibility function enables the detection of minor differences in speech in noise perception, and most DTT versions report measurement errors of less than 1.0 dB SNR for NH listeners. HI listeners have shallower

psychometric functions (Smits and Houtgast, 2007; Smits and Festen, 2011), and the measurement errors reported for HI listeners have been larger than for NH listeners, though mostly still within 1.2 dB SNR (Smits and Houtgast, 2007; Kaandorp et al., 2015; de Graaff et al., 2018).

2.2.2Comparability to other hearing measures

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statistically significant, but not perfect. The reported correlations range from 0.56 (Jansen et al., 2012) to 0.86 (Folmer et al., 2017). Some of the discrepancies may be due to different study populations; stronger correlations for PTAs and SRTs have been reported with bilateral

sensorineural hearing loss (SNHL) than with unilateral, asymmetric SNHL or conductive HL (De Sousa et al., 2021).

Other speech intelligibility tests

DTTs have been compared with both word-level (Leensen, de Laat and Dreschler, 2011; Vlaming et al., 2014) and sentence-level speech perception tests in noise in multiple languages (Smits, Kapteyn and Houtgast, 2004;

Jansen et al., 2012; Williams-Sanchez et al., 2014; Zokoll, Wagener and Kollmeier, 2017). Similar to studies on PTA, most studies with HI listeners have observed good (r > 0.70) and statistically significant correlations (Smits, Kapteyn and Houtgast, 2004; Jansen et al., 2012).

Most of the studies comparing DTTs and different speech perception tests in noise have included participants with mild-to-moderate HL, and testing has been carried out with headphones without hearing aids (HAs).

Fewer studies have compared DTTs to other speech perception tests in noise in CI users. The results of these comparisons have been more variable. Cullington et al. (Cullington and Aidi, 2017) reported a strong correlation (r = 0.76) between the DTT and BKB-SIN test (‘BKB-SIN Test’, 2005), while Kaandorp et al. (Kaandorp et al., 2015) reported only a moderate correlation (r = 0.56) between a sentence-level speech perception test in noise and the DTT.

Self-report questionnaires

The first data on the correlation of self-reported hearing disability and DTT results are from the NHT. All NHT callers were asked to rate their hearing on a scale from 1 (very poor hearing) to 9 (excellent hearing). Based on SRTs, and if compared to younger participants, elderly adults

overestimated their hearing ability. However, when the self-report data were analyzed in relation the overall performance of the participants’ age

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group, the estimations were more accurate. Similar data of elderly people underestimating their hearing loss based on the DTT results have been reported from another large-scale DTT study (Smits, Kramer and Houtgast, 2006).

Whereas elderly people seem to underestimate their hearing difficulty, data from people aged 40–69 from a large UK Biobank dataset reported that “A surprisingly high proportion of 40–50 y.o. people with normal DTT SRT indicated that they had difficulty hearing” (Moore et al., 2014). The UK Biobank data include SRTs from a short DTT (15 triplets) for both ears separately and answers to two questions on hearing (“Do you have any difficulty with your hearing?” and “Do you find it difficult to follow a conversation if there is background noise (such as TV, radio, children playing)?”). UK Biobank used the original landline telephone version of the DTT in which the test material was limited to 4 kHz, which may have rendered the test less sensitive to high-frequency HL. The researchers suspected that the bandwidth-limited version of the DTT was not able to capture all the perceived challenges of variable everyday listening

environments (Moore et al., 2014).

Modest correlations between DTT results and subjective hearing assessments were also observed with the South African smartphone application hearZA (De Sousa et al., 2018). In hearZA, listeners report whether they experience hearing difficulty (yes/no) before the start of the test. Of all the 17 611 listeners who had answered the question on hearing, 37% reported hearing problems. However, only 30.2% of these listeners failed the screening test. At the same time, 19.7% of the listeners who did not experience any listening difficulties failed the test. The data did show a clear increase in the SRTs with age, but the correlation of self-reported hearing difficulty to SRTs was not analyzed with respect to listeners’ age.

Some of the discrepancies between objective and subjective hearing assessments may be due to measurement error. Even though DTTs have shown to be sensitive and specific with good test-retest reliability, some

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measurement error is inevitable. For example, Smits et al. (Smits, Kramer and Houtgast, 2006) estimated that in an elderly population, NHT

misplaced around 17% of the screened participants into the wrong hearing-status category. If self-report questionnaire data are compared with these hearing categories, only 83% correlation can be expected at best.

Objective measures capture only one aspect of hearing, whereas subjective evaluations are also affected by other factors such as

personality and everyday listening environments. Pronk et al. (Pronk, Deeg and Kramer, 2018) explored what contextual factors might explain the discrepancies between self-report measures and DTT results. They found that, for example, self-esteem, the number of chronic conditions, and the number of depressive symptoms may alter a person’s reference frame and influence the way they experience (objectively measured) hearing loss.

They also observed that gender and self-efficacy to initiate behavior seem to be related to coping strategies used compensate for the hearing loss.