Professor Mark E Lutman is one of the UK's foremost experts in the field of noise induced hearing loss. Premextra talks to him about why this remains a relevant injury class today.
Before the 1970s, noise levels in manufacturing industry were much higher than today. There were also many more people employed in noisy jobs, including traditionally very noisy industries such as boiler-making, ship-building, weaving and carpet manufacture. Since then, aggregate occupational noise exposure has decreased substantially and it had been predicted that claims for noise-induced hearing loss would peter out.
In fact, the number of claims has remained high, according to Professor Mark E Lutman, of the Institute of Sound and Vibration Research University of Southampton. "Claimants generally have exposure to lower noise levels, often for many years," he says. "Consequently, claimants tend to be older with lower noise exposure. The combination of less marked noise-induced hearing loss and greater age-associated hearing loss makes it more challenging diagnostically to unpick the age and noise contributions."
Another consequence is that amounts awarded for loss of amenity are smaller, due to smaller components of noise-induced hearing loss. "These can be dwarfed by claims for special damages (mainly hearing aids)," says Mark, "developing a clear rationale for assessing increased need for hearing aids poses a further challenge. In addition, claimants commonly have complex employment histories, necessitating a justified rationale for apportionment of liability between employers."
On August 30 2012, Professor Lutman will present his research to delegates at the first of Premex's Expert Seminars. "My role in the seminar is to explore the scientific evidence base that underpins diagnosis of noise-induced hearing loss," says Mark. "In addition to understanding the pathophysiology of damage to the inner ear by noise, we rely heavily on epidemiological studies of hearing, involving either people exposed to noise or non-exposed "controls" across the age range. Because of the wide range of susceptibility in humans to age-associated and noise-induced hearing loss, there is substantial overlap between exposed and non-exposed groups. Therefore, diagnosis relies heavily on statistical inference and probability rather than a deterministic approach. I will also outline methodologies that utilise published probability information to reach a diagnosis on the balance of probability."
Professor Lutman says that medical experts have always faced the initial problem of obtaining reliable measures of hearing, where the main test (audiogram) relies on the claimant responding faithfully to the quietest detectable sounds. He explains the basic path for diagnosis: "Next, the expert must tease apart contributions from age, noise and any other identifiable components: this is generally the most difficult step. The incremental effect of the noise-induced component also needs to be estimated, both in terms of loss of amenity and need for additional treatment (e.g. hearing aids, tinnitus retraining therapy). There may be a further need to estimate the relative contributions from different periods of exposure, for the purposes of apportionment."
The need for solicitors to be able to rely on medical expert evidence has never been more pronounced, says Mark. "Diagnosis based on explicit probabilities may be unfamiliar to medical experts, although clinical inference often involves implicit weighing of the likelihoods of alternative diagnostic contenders. In a medicolegal context, it is important to explain the probabilistic basis clearly for the Court."