The danger of anecdotal evidence

Someone I know recently travelled to the New York area for a wedding. They stayed outside the city, and decided to rent a car with a GPS.

They used the GPS to get to the wedding, and it took them 35-40 minutes to get there.

On the return trip, the GPS originally planned the reverse route. As they were driving along, it ‘piped’ up that it had found a shorter route. They decided that they had gotten the GPS, so they may as well take advantage of it.

The new route involved driving through busy downtown streets. They were moving so slowly, they were able to purchase drinks and hot dogs from a sidewalk vendor. Three hours later, they arrived back at their hotel.

Now, if the story ended here, you would be inclined to think GPSs are very flawed, and a good old map would have served them better.

But, the story doesn’t end here. Family from the area, returning to the same location, took the reverse route the GPS had originally planned (i.e. the same route used to get to the wedding). It took them six hours to get back.

So, based on this, the GPS did accurately find a shorter route (and must have been tied into a traffic condition system).

I think we all know that anecdotal evidence is just that, but sometimes we put too much stock in it anyway.

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