Wednesday, June 18, 2014

2014-06-18: Navy Hearing Conservation Program Visualizations

(Note: This is the first in a series of posts about visualizations created either by students in our research group or in our classes.)

The US Navy runs a Hearing Conservation Program (HCP) which aims to protect the hearing and prevent hearing loss in service members.  Persons who are exposed to levels in the range 85-100 dB are in the program and have their hearing regularly tested.  In the audiogram, there is a beep sounded at different frequencies with increasing volume.  The person being tested raises their hand when they hear the beep and the frequency and volume (in dBA) are recorded.  A higher volume value means worse hearing (i.e., the beep had to be louder before it was audible). Not only are people in the HCP regularly tested, but they are also provided hearing protection to help prevent hearing loss.  The audiogram data includes information about the job the person currently holds as well as if they are using hearing protection.

Researchers are interested in studying Noise Induced Hearing Loss (NIHL).  The theory behind NIHL is that if you're exposed to a massive noise event, you lose lots of hearing instantly, but that if you're exposed to long-term noise, there could be up to a 5 year lag before you notice hearing loss.  One goal of the HCP is to track hearing over time to see if this can be identified.  Hearing in the 4000-6000 Hz range is the most affected by NIHL.

We obtained a dataset of audiograms from the HCP with over 700,000 records covering 20 years of the program.  From this, PhD student Lulwah Alkwai produced three interactive visualizations.

In the first visualization, we show frequency (Hz) vs. hearing level (dB) averaged by job code.  The average over all persons with that job code is shown as the solid line (black is left ear, blue is right ear).  Normal impairment in each ear is shown as a dotted line.  The interactive visualization (currently available at allows the user to explore the hearing levels of various job codes.  The visualization also includes representative job codes for the different hearing levels as a guide for the user.

The second visualization (currently available at shows the age of the person tested vs. the year in which they were tested.  The colored dots indicating hearing level use the same color scheme as the first visualization.  The visualization allows the user to filter the displayed data between all persons, those who used hearing protection, and those who used no hearing protection.  Note that this visualization shows only a sample of the full dataset.

The final visualization (currently available at is an animated visualization showing how age vs. total hearing (left ear hearing level + right ear hearing level) has changed through time.  Once the page loads, the animation begins, with the year shown indicated in the bottom right corner.  The visualization is also interactive.  If the user hovers over the year, the automatic animation stops and the user takes control of the year displayed by moving the mouse left or right. As with the previous visualization, this shows only a sample of the full dataset.

We created a short demo video of all three visualizations in action.

All three of these visualizations were made using the D3.js library, using examples from Mike Bostock's gallery.  The animated chart was based on Mike Bostock's D3.js recreation of the Gapminder Wealth and Health of Nations chart.


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