ben white

The NBME Shelf exams are enjoyable standardized tests that every first year looks forward to with almost unbearable glee. They test a single subject (“Anatomy”) and apparently take the relevant questions from the USMLE Step 1, a test that makes the MCAT look like the GRE and the SAT look like building with Lincoln logs.

Some schools force their students to take a variety of Shelf exams (spending/wasting $30 a pop) to help measure how well their students have mastered the material (AKA how they are doing compared to their national counterparts). What is a bit amusing and misleading about the whole ordeal is that the national norms are probably a big crock.

Different schools use the “shelves” differently. Some use them as a just-for-fun intellectual exercise, others as extra-credit, and still others as a true final exam. Don’t get me wrong, it’s not a bad thing to get some USMLE Step 1 experience, but it’s highly dependent on the environment: if you take five step exams in a single week, you are clearly not going to be prepared or even particularly focused. If it’s your final exam, you are going to do your best to rock it.

So if the national average is computed from all of these groups together, then it’s going to have a huge unseen left tail: if people are taking the exam who don’t care how they perform, they’re going to be dragging the average down from where it would otherwise be. So while the test is technically normalized, it’s not the same normal as a regular standardized test: Unlike the MCAT, not every student has something riding on the exam. I personally knew people who filled out all C’s on an exam that was for extra-credit only.

While your school receives the group’s average and your grade relative to your test group (classmates), the theoretically more interesting numbers a student receives are the grade based on the national average and corresponding percentile. I’m curious as to how far off the scores really are. If all those people who weren’t making a good faith effort actually tried (as they do on the USMLE Steps 1, 2, 3), then I’d wager it’d be a different ball game. It’s essentially an unstandardized standardized test.

A X-year-old [type of person] reports to the doctor/ER with a X-hour/day/week/month/year history of not-feeling-so-hot. Upon examination, distracting details. Irrelevant information. Single key relationship. More words to make the test take longer. Talkie-talkie. What is the likely cause of this you-should-have-learned-in-your-class-and-probably-did-but-maybe-you-didn’t-who-knows-there-are-so-many-questions-on-this-test-it’s-all-a-blur person’s problem?

Every few months, I see some news report on the revelation that listening to loud music can cause hearing loss.  Yesterday, Time online posted “iPod Safety: Preventing Hearing Loss in Teens,” the latest in this series of mediocre ear-science.  I’ll admit that in this case the facts are accurate, it reminds me of a lot of stories that are less so.

The point, which is true, is that listening to loud noises of any kind tends to be bad for the ears. The louder the noise, the less time it takes to cause damage. Prolonged exposure to loud noise leads to both tinnitus (ear-ringing, which sucks) and sensorineural hearing loss (which sucks and is irreversible). This is actually a serious problem, and it’s caused the kind of hearing loss in teens that used to be reserved for old-time factory workers. My beef is that there is one finding several years ago that has given rise to a huge misconception:

In-ear head phones generate more sound pressure at a given volume setting than over-the-ear counterparts [source].

This is logical, given that in-ear headphones are actually in your ear, literally closer to your tympanic membrane, which transmits the physical pressure waves to your middle ear. Because iPods are generally used with in-ear headphones, some news outlets and people came away with the idea that in-ear headphones are automagically more dangerous—which is hogwash.

This is silly because pressure and volume are essentially the same thing. When the in-ear headphones produce more “volume” at a given setting, the user actually hears the music louder. If I were to switch from over-the-ear to in-ear phones, chances are I’d adjust the volume accordingly. The fact that earbuds can pump out more decibels in and of itself is meaningless. Admittedly, there has been some work that has shown that some earbuds don’t cancel external sound all that well and therefore might lead to higher volumes when used, but this varies wildly between brands. All that means is that the government should subsidize some new Bose headphones for people who work in loud places, because good sound-canceling headphones are the only ones that eliminate this problem effectively. Being closer to the ear is not an inherent problem unless the volume isn’t adjusted accordingly. This is not an unnoticeable danger increase.

What studies have shown is that individuals have a preferred ambient listening volume. Some very angry teenagers who like thrash metal tend to like to blow a hole out of their eardrum, but the rest of us tend to fall somewhere on a decent curve. What matters is what relative volume we prefer, not what method we use to get there. When people taken off the street were tested for average listening volume, the data reflect this reality: the biggest problem is background noise. We tend to like our music somewhere around 60dB. If the ambient noise is 20dB, many people will turn up the volume to 80dB. If you correct for background noise, preferred volume is nearly constant. So when people listen to their iPod somewhere loud (on an airplane or the subway), they’re probably doing a lot more damage than if they’re at home. It really is that simple.

The idea that in-ear headphones are actually worse for you is based on this distortion. They’re not; your preferences and habitat may be.

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