1. Why use statistics?

The best-known statistical tool is certainly the average. From the start of our schooling, we've been used to calculating the average of our grades, the class average and so on. From a mathematical point of view, it's quite simple and unambiguous. And the result is exact, because we know all our grades or all those of the class.

But in our professional activity, it becomes very difficult, even uneconomical, to know all the measurements of each product or each elementary activity. On the other hand, we can have access to information on a few products or activities - what we call a sample. We can calculate the average of this known sample. The question we need to ask ourselves is to what extent this average is representative of the average for the entire population.

If we make decisions on the basis of this average, what risk do we take of...