Researchers develop a new way to track progress in curbing hearing impairment, find that self-reporting needs to be supplemented by more direct testing
July 6, 2009–Americans are hearing better today than they were 30 years ago, but progress on reducing hearing loss has slowed, according to a new study, Tracking population health based on self-reported impairments: trends in prevalence of hearing loss in US adults.
Researchers at the Institute for Health Metrics and Evaluation (IHME) at the University of Washington and at the Harvard School of Public Health found that the rate of hearing loss decreased dramatically in the 1990s, from a high in 1993 of about 12.2% of all men and 7% of all women to a low of 8.1% and 4.2% respectively in 2000. Since then, hearing loss has remained about the same, indicating that efforts to prevent hearing loss through noise reduction and better hearing protection in high-noise work places have hit a wall.
“You can see steady improvements throughout the 90s, and then it just stops abruptly,” said Nayu Ikeda, a research fellow at IHME and the study’s author. “We would need more research to understand exactly why, but it suggests that hearing loss prevention efforts have only worked up to a certain point.”
The study, published in the American Journal of Epidemiology on July 6, presents a major advance in the way trends in hearing impairment are recorded and tracked in the US. Previous studies have shown wide variations in the prevalence of hearing loss. In 1999, for example, the hearing loss among men was estimated at 25.9% in one survey, 16.2% in another and 7.5% in a third.
“There is a lot of disagreement across surveys and even within some of the same surveys over time,” said Joshua A. Salomon, an associate professor of international health at the Harvard School of Public Health, another author on the study. “With these huge differences, it was hard to know how things were really changing over time, so we wanted to use all of the available data to find the true trend.”
Working with Salomon and IHME Director Christopher J.L. Murray, Ikeda developed a methodology for standardizing the surveys. The team studied interviews and hearing loss tests from four nationally representative surveys conducted regularly between 1976 and 2006. Their research took into account nearly 1 million surveys.
The researchers found that variations in hearing loss trends were rooted in part in the design of the surveys. Most hearing loss studies rely on interviews, and the IHME study found that when people are asked to rate their hearing on a five-point scale they tend to give themselves lower marks than actual hearing tests indicate. If people are asked to give yes/no answers instead, the results are mixed, depending on the age or gender of the respondent.
For the IHME study, the team augmented the survey data with audiometric hearing-test data from the US Centers for Disease Control and Prevention’s National Health and Nutrition Examination Survey to arrive at the most accurate count to date of hearing loss in the US. Audiometric hearing tests require people to respond to sounds played through headphones to test their sensitivity to both tone and volume.
Although it is considered the gold standard for measuring hearing loss, audiometric testing has been used much less frequently than self-reports, the study found. Out of 990,609 people who participated in hearing loss studies since 1976, only about 5,300 were given the headphone tests. By finding the ways that self-reported measures differ systematically from the audiometric tests, however, the researchers were able to estimate how many people with hearing loss were being missed by the self-reported surveys.
To understand why the trend in hearing loss reduction has flattened, the researchers propose that workplace regulations in the 1990s reduced exposure to hazardous levels of noise and that further study of regulations and prevention programs may be needed to continue the downward trend.