How understanding the difference between type i and type ii errors can get strange men out of your house

This is the second installment in a series of blog posts in which I discuss data science related topics with an overly familiar stranger. Here are parts 1 and 3.

Pssst!

Huh?

Pssst!

Wha?

Ayo my man!

What? What are you doing in here?

Ayo my man, is that any way to greet your friend?

Friend? I’ve met you a grand total of one time and —

More than enough to be a friend.

AND you’re not only in my house uninvited, but you’re in my bedroom.

What do you want?

Wait, are you eating my food?

Big dog’s gotta eat, right?

I suppose, big dog.

It’s like this my man, I’m not too fond of how our last encounter ended, right?

Okay…

And I gotta get back my honour —

I would’ve thought a guy who snuck into a person’s room in the wee hours of the morning didn’t have much of that.

And I’m gonna do it with another riddle.

You got to be joking.

So you got this group of 100 old geezers, right?

Out of curiosity, how old are we talking here? Greatest Generation old or I’m past my physical peak but I can still run a marathon old?

Don’t matter. Let’s just say they’re old. So old that when people see them on the street they’re like, “Yoooooooo! Those dudes are old!”

Alright.

So, like I was saying, real geezers and every single one of them got bladder issues.

Where is this going?

It’s going right here, but before it does, why are you acting like you got places to be my man? You in bed ain’t you?

Is this the part where you get to the riddle?

I’ma ignore your rudeness and get to my riddle. So some of these guys look like they’re about to wet themselves, right? So you make predictions on who’ll have to use the bathroom within 10 minutes.

That’s kind of a strange thing to be predicting don’t you think?

The only thing that’s strange is you thinking it’s strange, my man.

If you say so.

Anyway, you make predictions on who’ll use the bathroom.

40 of the guys you say will use the bathroom use the bathroom.

20 of the guys you say will use the bathroom don’t use the bathroom.

15 of the guys you say won’t use the bathroom use the bathroom.

25 of the people you said wouldn’t use the bathroom don’t use the bathroom.

Now, how many of your predictions are false negative, true negative, false positives, and true positives?

Did you seriously wake me up in the middle of the night for a Type I and Type II error problem?

You damn right I did.

You said that with a surprising amount of conviction.

And you’re doing a surprising amount of stalling.

I’m not really stalling. The answer is pretty simple.

Then why haven’t you given it to me yet, my man?

As I was saying, the answer is pretty simple. I just have to do two things:

• For the true or false part, ask myself whether I was right.
• For the positive or negative part, ask myself what I predicted.

I don’t like where this is going…

Accordingly, the 40 guys I predicted to use the bathroom who did use the bathroom are true positives.

The 20 guys I predicted to use the bathroom who didn’t are false positives.

The 15 guys I predicted to not use the bathroom who did are false negatives.

And, drumroll, the 25 guys I predicted to not use the bathroom who didn’t use the bathroom are true negatives.

Ayo my man, you know I hate you, right?

I’ll see myself out.