Sunday, October 2, 2011

Groundhog Day - A Little Science

Groundhogs day is the second of February, where groundhogs emerge from their burrows early in the morning. Once they're out of the burrow they do one of two things: either they continue with what they started, or they go back for 6 more weeks.

The legend says that when they emerge in a sunny day and they see their shadows they predict 6 more weeks of harsh winter and decide to hide in their burrows for 6 more weeks. If that day is cloudy and they don't see their shadows they predict a nice spring weather in 2 weeks and they stay.

Money wise it's a nice idea. People gather early in the mornings for the groundhogs day festivals where they are celebrated and tourists spend money on their transportation, accommodation, food, and entertainment. Relying on those predictions is another story.

Let's use a little bit of science. The critter was hiding under the ground for months, where its dark. Naturally when they go out and it's too bright on a sunny day their eyes are not going to take it. Also naturally when they get out of their burrows they look towards the north west where the sun is to their backs. And this direction where they're looking is where their shadows are, so whether they see their shadows or not, this is where they are looking.

On another level, the predictions made by people watching the behavior of groundhogs on this day are not always accurate. In fact, they are only accurate 37% of the time. Now let's remember some of the probability math we studied in the school. We have four variables here: sunny vs. cloudy, and good weather vs. bad. From the behavior of the animal sunny groundhogs days are always accompanied by a prediction of bad weather, and cloudy days are linked to good weather.

This reduces our variables to only two: sunny days with prediction of bad weather vs. cloudy days with good weather coming ahead. This is exactly like the two probabilities in throwing one coin. Each side gets 50% chance of showing on top every time you throw it.

Compare that to the accuracy of the weather predictions made by the groundhogs event planner. This is not even as good as throwing a coin.

But at the end of the day it's a nice tradition that keeps people attached to nature and to mother Earth a way or another, which is a very attractive outcome of the event if nothing else.

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