# Pitfalls in the Detection of Hearing Loss via Otoacoustic Emissions
## 4 Discussion  
Many commercial OAE screening systems work as a \"black box\", and so users have an incomplete knowledge about how they function. The stimulation parameters (stimulus shape, level, polarity), the recording properties (windows, filters), and the analysis method (criteria for classification) remain usually unspecified in the user manual, presumably because of copyright issues and technical patents. This study attempted to uncover some of these properties by comparing results from two versions of the Accuscreen OAE device and the ILO system. The motivation was that presently there are only a few papers in the literature that present data comparing different OAE systems. For example, in a study of two types of ILO systems, a screening and a clinical type, agreement above 90% was reported [17]. [PERSON] et al. reported a very high level of agreement (nearly 99%) between an ILO-88 and the Madsen EchoScreen, a predecessor of the Accuscreen [15]. Such results, as well as a scarcity of newer studies and shortage of information, have created the erroneous impression that there is good agreement between measurements from different OAE systems. Our data show that there were significant differences in TEOAE evaluation as assessed by the old and new versions of the Accuscreen device, even though they are from the same manufacturer. Differences were also observed when the Accuscreen devices were compared with the ILO-292 system. Agreement between both Accuscreen devices was gauged as moderate (77.3%, \(\kappa=0.54\)), similar to the level of agreement (70.8%, \(\kappa=0.44\)) between the older device (Accu 1) and the ILO. Only agreement between the newer device (Accu 2) and the ILO was gauged as acceptable (80.5%, \(\kappa=0.61\)). The best point of comparison for our results that we could find was a Food and Drug Administration report [30] that compared the new Accuscreen evaluated here (Accu 2) and the EchoScreen, which is the predecessor of the older version of Accuscreen (Accu 1). The disadvantage of this study was that it involved only a small study group. Nevertheless, for adult subjects, agreement of around 86% was achieved, which is slightly better than the agreements achieved here of around 70-80%. In terms of audiometric results, the disagreement between the Accuscreen devices occurred most frequently in ears with higher thresholds in the 1-8 kHz range and where thresholds below 1 kHz were still within the norm. The newer version of the device (Accu 2) performed better than the old (Accu 1). We can only suppose that the TEOAE analysis method was improved in the new version. The biggest weakness of both devices is that they provided a pass to ears with a threshold elevation >25 dB at 8 kHz. However, this is not surprising in that the majority of TEOAE probes have a frequency response limited to 4-5 kHz. In addition, from previous studies, OAEs (especially TEOAEs) are generally known to perform best over only the 1-4 kHz range [31]. Indeed, the discriminant analysis revealed that the most important audiometric frequencies in terms of pass/refer results were 1, 2, and 4 kHz, which covers the TEOAE range. This range also includes the greatest slope for the group of ears for which the results were different (Figure 1). When the SNRs from the ILO were used in the discriminant analysis, it showed that the most important frequencies were 1.4 and 2 kHz. This is probably related to the fact that adult TEOAEs present higher amplitude levels in the 1-2 kHz range. It is also relevant that these frequencies are also dominant in speech, and so the presence of OAEs in this range may indicate good speech understanding; however, this cannot be generalized to cases of auditory neuropathy or disturbances to auditory brainstem responses (ABRs) [32]. For ears with weak TEOAEs, a response above 2 kHz may not be present, and in the 1.4-2 kHz range it can be very small.