ELI5: Explain Like I'm 5

Determining the number of clusters in a data set

Alright little buddy, imagine you have a lot of colorful candies like M&Ms, Skittles, and Smarties. You have a big bag full of all these different candies, but you want to organize them by their colors. How many groups can you make?

Now, let’s say that you don't know the colors of these candies, but you can sort them by some similarities, like maybe size or shape. You don't want to put different candies together because they might taste different.

So, if you have a lot of candies that look similar in one group, and then another group of different candies that look different, you can say you have 2 groups. If you realize that there are more groups, you can name them.

This is what happens when we try to group data that resemble each other. Each group of data is a cluster, just like each group of candies was a cluster. This is what we call clustering or cluster analysis.

But how do we know how many clusters we should group our data into? Well, this is where it gets a little bit more complex little buddy. You know, because it’s science!

We use something called the ‘Elbow Method’. It sounds strange, but it's actually pretty cool. It's like a game we play to see how many groups our data should be in.

Think of your graph paper, and imagine that every data point represents one of your candy pieces. Now draw a line graph where you plot how similar the candies are in each group against the number of groups you’ve made. On the X-axis, you put the number of groups you made, and on the Y-axis, you put the similarity between the candies.

This graph will look like a hill or a mountain range. But there will be a point where it seems like the line graph drops down like the end of your elbow. You know, where your arm crunches up. This is where the name, ‘The Elbow Method’ comes from.

That point, where the line graph drops down, is the point where we can say we have the optimal number of groups or clusters for our data. Pretty cool, huh?

So, in conclusion little buddy, we have a lot of data like candies, and we want to organize it. To do this, we make groups or clusters of similar data. The best way to figure out the number of clusters is by playing a game called ‘The Elbow Method’. It’s like finding the perfect number of groups for our candy pieces.