NOBODY IS PERFECT

Nobody is perfect

Or, in other words, we all make errors. Let’s see the types we can make:

Suppose you are testing the effectiveness of drug A compared to drug B. There are two real possibilities: either there is a difference between them or not.
After you perform the test, there are two possibilities: either you FIND a difference, or not.
You could put that in a 2x2 table:

                                   Real difference    No real difference
Computer says YES      Well done!         Type I error
Computer says NO      Type II error      Well done!

There are two ways you can go wrong. If you affirm there is a difference between A and B, and there is not, you have a type I or alpha error. If you are not able to find a real difference between A and B, you have a type II or beta error.

You can put it in other words:
If you reject a null hypothesis but you should have accepted it, you fall into a type I or alpha error. If you accept a null hypothesis but you should have rejected it, that’s a type II or beta error.

There is a mnemotechnic for it; Beta stands for Blind. (Beta error means you are blind to see a real difference between the two drugs).


Thanks for reading!