Exciting Trends…and Algebra!

Open fittings utilizing behind-the-ear (BTE) instruments have gained popularity in the past 2 years, and BTE fittings now make up an amazing 42% of the market, according to Hearing Industries Association (HIA) statistics for the first quarter of 2006. In February, HIA conducted a special survey of members and found evidence that open fittings are likely to constitute about 12% of BTE fittings. Preliminary data from the HR 2006 Dispenser Survey (to be published in June) confirms that BTE usage has spiked, and that open-fit devices are used by hearing instrument specialists in about 15% of their BTE fittings and by dispensing audiologists in about one-third of their BTE fittings. Whatever the actual percentage, open fittings are gaining steam quickly, and are a good example of how fast-paced hearing aid technology is becoming. ReSoundAir was launched in 2003 and, although not the first open-fitting hearing aid, the product line was arguably the first in the new century to find commercial success using open-fitting concepts. Today, most hearing instrument manufacturers not only have BTEproduct lines that can be converted (via earbud adapters) into open-fitting systems, but many also possess dedicated open-air product lines.

Likewise, directional technology has taken the industry by storm, also contributing to higher usage of BTEs. According to the same HIA survey, 35.2% of all hearing aids sold in 2005 contained directional systems, and almost half (47%) of all BTEs utilized directional microphones. In this issue of HR, David Fabry, PhD, presents an interesting perspective on facts versus myths related to open fittings and directional systems.

Math nerds unite. My half-hearted commitment to learning higher mathematics in college (I once blew off studying for a calculus course to finish reading The Red Badge of Courage) came back to haunt me yet one more time this month. For years, it has been a mystery to me how to calculate the number of purchasers of hearing instruments when provided with the total number of units sold and the monaural/binaural ratio. It seems like an easy problem to solve: Take the percentage of monaural users multiplied by the number of units to get the number of individuals who are monaural users. Then simply subtract this figure from the total number of hearing aids and divide the remainder by two to get the number of binaural users. Violà! Incorrect answer. I finally contacted statistician Dick Green, an associate professor at the University of Minnesota, Duluth. For anyone who has ever wondered how to convert units to fittings in your practice, here is the answer:

First, let y be the number of people fitted for hearing aids. The number of hearing aids must equal the number of monaural aids plus the number of binaural aids, so:

([binaural percentage] x 2 x y) + ([monaural percentage] x y) = [number of hearing aid units]

So, for example, if there were 1,899,785 units dispensed by private practices/offices during 2005, and there was a binaural:monaural fitting ratio of 73:27, then…

(0.73 x 2 x y) + (0.27 x y) = 1.46y + 0.27y = 1.73y = 1,899,785 and…y = 1,899,785 / 1.73 = 1,098,141.62 or 1,098,142 people fitted with hearing aids. Now it’s easy:

To find the number of people fitted monaurally: 0.27 x 1,098,142 = 296,498 peopleTo find the number of people fitted binaurally: 0.73 x 1,098,142 = 801,644 people

Green says that, in this particular problem, since 1% of almost 2 million is about 20,000, it is unwise to take the final monaural /binaural numbers too literally; rather, “they should be thought of as plus-or-minus 10,000 or so,” he advised. He also was kind enough to humor me by saying it was a deceptively complex algebra problem. Well, that concludes our Math Club meeting. Now put your pocket protector back in your shirt, retape the bridge on your glasses, and get back to work.