Wednesday, 2 March 2011

Normally Distributed



Another nice statistical curiosity from the Statpics blog of Professor Robert Jernigan at American University.  The entire short post is copied below, and I would love to hear responses to the final question.  And it also looks like the wear on the left door is distinctly heavier than the right..do you agree? and if it is...why?  Do we go out with our left and in with our right, or ??? Anyway, here is the Professor's blog:
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An image of the wear on exit doors at a Barnes and Noble bookstore in Rockville, Maryland. Most wear is located a little below shoulder height as customers push on the door with outstretched arms as they exit. Or are they holding open the door with fingers as they enter? It turns out it's both. (Yes, I stood there and watched!). It's both uncomfortable and inefficient to open the door much higher or much lower. We're left with a greater frequency of use centrally located with less and less wear above and below: a unimodal frequency distribution of wear. Considering that human height is approximately normally distributed, the patterns here should reflect that normality. It's interesting to note that the left hand door seems to have a frequency distribution of wear that sits slightly above that for the right hand door.
Any ideas as to why?
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http://www.armstronglock.com/images/prod-0101383-zoom.jpgAddendum: MLB sent a comment with a couple of ideas that were too perfect to leave in the comments.  Another cool place where a similar unimodal distribution pattern shows up is on Jerusalem's Western Wall:

Finally, this phenomenon is the reason why these sort of locks are unsafe:  One time I was with a group of people locked out of a building. A member of our group had left something inside, and none of us had a key. There was a lock box, though, and some careful observation of the exterior of the box gave us some good guesses as to the combination. We got in without trouble.

2 comments:

Steven Colyer said...

Here's my answer, and bear in mind this is only a guess:

Most people are sheeple, thanks to our culture that encourages "proper" behavior. Nevertheless, at heart we are individualists. Therefore, when we can, we break rules, as long as they're small ones that don't hurt anyone. Therefore, since we know the "proper" door to exit through is the right-sided one, we subconsciously exit through the left if no one else is coming in. If someone is approaching the door as we approach the exit, we revert to proper-ness and use the right door. Unhappy that we are forced, yet again, to be conventional, we don't lift our arms as high. If no one else is coming though, we're happier at being a rule breaker, and lift our arms higher when exiting the left.

Or maybe most spaces in the parking lot are on the left side of the door, and we seek the door closest to our vehicles. ;-)

MBP said...

Here's my guess: People are holding their bags or purchased items in their favored hand as they leave or enter. For most people, that means that their right hand is occupied, and only their left one is free to push or pull the door.

Another cool place where a similar unimodal distribution pattern shows up is on Jerusalem's Western Wall: http://www.levitt.com/slideshow/s01p05.jpg.

Finally, this phenomenon is the reason why these sort of locks are unsafe: http://www.armstronglock.com/images/prod-0101383-zoom.jpg. One time I was with a group of people locked out of a building. A member of our group had left something inside, and none of us had a key. There was a lock box, though, and some careful observation of the exterior of the box gave us some good guesses as to the combination. We got in without trouble.