The Confusion with Confusion Matrices

If you're like me, who gets confused with confusion matrices no matter how many times you have used them, then probably this post might help you, and myself included.

Type 1 and Type 2 Errors

Sometimes in the literature, you'll see False Positives and True Negatives as Type 1 and Type 2 errors. Here is the correspondence:

• Type 1 Error (Error of the first kind, or False Positive): In the medical example, this is when we misdiagnose a healthy patient as sick.
• Type 2 Error (Error of the second kind, or False Negative): In the medical example, this is when we misdiagnose a sick patient as healthy.

But confusion matrices can be much larger than $2 \times 2$. Here's an example of a larger one. Let's say we have three illnesses called A, B, C. And here is a confusion matrix:

So if we have a medical model below which classifies a healthy from a sick patient.

The confusion matrix will look like the table below for 10,000 patients.

Huge thanks to Udacity on this one! I might sound like I'm advertising this website (they're good tho), but give credit where credit is due. :)