Thursday, December 5, 2013

Correctly Interpret Data And Statistics

A small detour from my usual subjects...

A common statistic came into my mind today. "Most car accidents happens near the driver's home". Sorry that I do not have a link to this statistic, but in my country that has been said more than once.

It has led people to believe that we are usually more careless or distracted when driving near our homes. Maybe because we are in a hurry, anxious to get to our beloved house and people, or because we are just leaving, not yet fully connected to the action of driving.

I beg to differ; I think this is a misinterpretation of the data. Let's think about it: when you go to work, what streets do you necessarily take? At least the one in front of your home (if you have more than one exit, well, you are blessed, aren't ya? But follow the thought). When going to the supermarket, the mall, a concert, your parent's house, etc., what streets are common in those trajectories? The ones around your home, of course! At the end and beginning of almost every day you are driving around your home.

So, let's assume for a second something more, well, conservative. That the probability of having a car accident on any given street is the same, at least on average. Now, since you are driving near your home much more than you are driving anywhere else, indeed, the probability of an accident in this vicinity is higher!

I'm not saying that distraction may not be a factor here. Those two conclusions are almost equivalent. I'd say that mine seems a little more fundamented of factual, consistent affirmations (since I'd not had to infer that people were distracted), but in any case, if there are at least two reasonable explanations to this data, then it become useless; We need more detail to check whether being near our home makes us worse at the wheel.

Whenever you are fed data and statistics like this, try to interpret it with fresh eyes. Many people just swallow what the media says, and do not question conclusions that, many times, are not made by specialists but by journalists that need to continuously produce news of some sort.

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