Why is statistics difficult?

Imagine you are somewhere on a road that you have never been on before. Picture it. It’s peaceful and calm. A car comes down the road. As it gets to a corner, the driver appears to lose control, and the car crashes into a wall. Fortunately the driver is OK, but they can’t recall what happened.

Let’s think about what you experienced. The car crash might involve a number of variables an investigator would be interested in.

• How fast was the car going? Where were the brakes applied?
• Look on the road. Get out a tape measure. How long was the skid before the car finally stopped?
• How big and heavy was the car? How loud was the bang when the car crashed?

These are all physical variables. We are used to thinking about the world in terms of these kinds of variables: velocity, position, length, volume and mass. They are tangible: we can see and touch them, and we have physical equipment that helps us measure them.