ELI5: Explain Like I'm 5

Pignistic probability

Okay kiddo, have you ever played a guessing game? Sometimes you might have to guess what's inside a box, or how many candies are in a jar. But you don't always know the exact answer, right? That's where pignistic probability comes in!

Pignistic probability is a way of guessing how likely something is when you don't have all the information you need. It's a lot like making an educated guess, based on what you do know.

Let's say you have a jar of candies, and your mommy tells you that there are red, green, and blue candies in the jar. But she doesn't tell you how many of each color there are. You really want to know what your chances are of picking a red candy out of the jar.

So, you start to think. You know there are three colors, and you know there are candies of each color. Since you don't have any other information, you might decide that each color is equally likely to be picked. That means you would have a one-third chance of picking a red candy, because there are three colors in total.

But let's say your mom then tells you that the jar has twice as many blue candies as red candies. Now your guess of one-third isn't right anymore. But you can use pignistic probability to adjust your guess based on this new information.

First, you have to translate what you know into a probability distribution. This basically means putting numbers on each possible outcome based on how likely you think it is. So, your possible outcomes in this case are picking a red candy, a green candy, or a blue candy. Each color was equally likely before, so you could assign a probability of 1/3 to each. But now that you know there are twice as many blue candies as red, you might change that probability to 1/5 for red (since there are now five candies of each color total), 1/3 for green, and 2/5 for blue.

Now, you can use a formula to calculate the pignistic score for each color. This is basically a way of combining your probability distribution with a "belief function" that tells you how much you know about each color. For example, you might believe that red is less likely than green or blue, because there are fewer of them. The pignistic score for each color is the sum of the probabilities for that color multiplied by your belief in that color.

Finally, you can use those pignistic scores to make a new guess about how likely it is that you'll pick a certain color. In this case, you'd find that your new guess is around 23% for red, 37% for green, and 40% for blue. So, you might decide that you have a slightly better chance of getting a blue candy than you thought before!

And that's pignistic probability for you, kiddo! It's basically a way of making an educated guess based on the information you have, even if you don't know everything you'd like to.