Editing 1236: Seashell

{{comic
| number    = 1236
| date      = July 10, 2013
| title     = Seashell
| image     = seashell.png
| titletext = This is roughly equivalent to 'number of times I've picked up a seashell at the ocean' / 'number of times I've picked up a seashell', which in my case is pretty close to 1, and gets much closer if we're considering only times I didn't put it to my ear.
}}

==Explanation==
This method of relating the probabilities of two events is known as {{w|Bayes' theorem|Bayes' Theorem}}.

If you put a {{w|seashell}} up to your ear, you might hear {{w|Seashell resonance|a sound similar to the ocean}} apparently inside the shell. But the idea that this sound is actually the sound of the sea is just a popular myth: hold only your hands close to your ears and you will hear the same sound, as it is the sound of your blood moving through your blood vessels that causes the sound. The comic, through an application of Bayes' Theorem, points out that most of the time when you pick up a seashell, you are in fact at the beach next to the real ocean, so hearing the ocean at that location is not all that impressive, but it's just real.

The equation should, however,  be read as follows: (The probability that I'm near the ocean, given that I picked up a seashell) is equal to (The probability that I picked up a seashell, given that I'm near the ocean) multiplied by (The probability that I'm near the ocean) divided by (The probability that I picked up a seashell).

The title text points out that most instances where the author has picked up a seashell have been at the beach, and nearly all of the times where he has picked up a seashell and put it to his ear have been there.

This comic was released late. In the first version, the formula was incorrect, but it has since been corrected.

==Transcript==
:[At the top of the panel is an equation showing Bayes' Theorem for the probability that a person is near the ocean given that they just picked up a seashell.]

:P(I'm near the ocean|I picked up a seashell) = 

:P(I picked up a seashell|I'm near the ocean)P(I'm near the ocean)
:------------------------------------------------------------------------------------------------
:P(I picked up a seashell)

:[The probability that I'm near the ocean given I picked up a seashell equals the probability I picked up a seashell given I'm near the ocean times the probability I'm near the ocean all divided by the probability I picked up a seashell.]

:[Cueball holds a seashell and stands to the left of the panel, to the right, a few birds are flying around and the sound of a wave crashing against the shore is depicted.]
:''Crashhh'' ''Sploosh''

:Statistically speaking, if you pick up a seashell and ''don't'' hold it to your ear, you can probably hear the ocean.

==Trivia==
Note that while this form of Bayes's theorem is often taught in statistics classes, [https://www.springer.com/gp/book/9783319397559 at least one statistician] tries to show in a philosophical way that unconditional probability does not exist, which would make the equation improper as stated.

{{Comic discussion}}
[[Category:Math]]
[[Category:Statistics]]
[[Category:Comics featuring Cueball]]