## Using Statistical Techniques

This story is a fable about the danger inherent in simply imitating a statistics teacher without understanding what is being taught.

Among the new faculty hired at the University of Edinburgh one year were three statisticians and three engineers. Now, Edinburgh is not a cheap place to live, and so all six of these new faculty ended up out on the edge of town, taking the train in every morning.

The first day of classes the engineers, with a deep understanding of tolerances and safety margins, arrived well before the train and purchased three tickets. The statisticians, who understand the importance of getting enough sleep, arrived just before the train and purchased a single ticket. One of the engineers, noticing this, asked the statisticians if this was a sensible course of action. The statistician said simply "watch, and learn".

The statisticians all got onto the same car well back from the front of the train. The engineers, curious to see what would happen, also found seats in that car. When the conductor was reaching the end of the next car forward, all three statisticians got up and went into the washroom. The conductor, noticing the washroom was engaged, knocked on the door, loudly calling for a ticket. A ticket slid under the door and the conductor continued into the next car.

The engineers were properly irked by this conduct, in part because of the poor design of the system for ensuring fares were properly collected, but also because they paid more for the trip into work. Solidarity among colleagues (and the general awkwardness of explaining what had happened) kept the engineers from turning in the statisticians. Instead the engineers ate lunch together and devised what they thought was a cunning revenge.

The next morning the engineers arrived safely early and purchased a single ticket. The statisticians, arriving just in time, purchased no tickets. One of the engineers inquired in an outraged tone how this was going to work. One of the statisticians replied again, "watch and learn".

The engineers chose the same car that the statisticians had the day before and immediately occupied the washroom, obstructing the statisticians' ploy of the previous day. One of the statisticians waited a few minutes, walked down to the washroom, and rapped sharply on the door, demanding a ticket. When the engineers slipped their ticket under the door, he pocketed it and rejoined his colleagues. The engineers resumed their seats with some smirking. The statisticians politely smiled back and then piled into the washroom as the conductor hove into view at the back of the next car. The rest of the scene played out the way it did the day before, except that the engineers were charged the special high price for tickets sold on the train.

### The Moral.

Never use a statistical technique unless you understand how it works.

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