Precision, Recall and F1 score (information retrieval)

Suppose we are playing a words game: I think a few words and you have to guess them.
As usually you will ask me some questions, identify the subject and try to guess. A possible end of the game is:

  • I think: rabbit, carrot, orange.
  • You try: dog, carrot, peach, orange.

We can define 2 quantities to synthesize how good you are as this game:

  • precision: is the number of correct guess over the number of tries = 2/4
  • recall: is the number of correct guess over the number of words to guess = 2/3

It’s easy to see that this two numbers are somehow in competition.

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