NLP 101: Understanding Precison and Recall

If you’re dealing with NLP, you better know the terms precison and recall. If that’s not the case, however, read on! There’s always got to be a first time!

The Brain Game

Let’s say I want to test your memorization skills, so I ask you to play a brain game. The game is simple. I show you a bunch of objects, and all you have to do is remember as much of them as possible. Easy? Cool. Time’s up. Let’s test you out.

Let’s say you call out a bunch of items H = {h1, h2, … hm}, while I actually showed you T = {t1, t2, … tn}.


Recall, quite simply, is how much do you correctly recall!

So out of the H items you think you saw, you only recall H∩T of them correctly. How many of the T items did you actually remember? Yup, that’s your recall rate.


Precision is how often do you get your judgements right.

So out of the |H| attempts you make, you were right only |H∩T| times. Your precision?

Easy, right? So if you ever have a hard time with this again, just remember the brain game we played.


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