So we call this the first quartile, the second quartile, the third quartile and the fourth quartile.

This is where you'll find the lower quartile, the median and the upper quartile.

These two elements over here are called the lower quartile and guess what the upper quartile.

What are the characteristics of this top quartile?

The formula is we have to four quartiles, 4 times n plus three separating elements the lower quartile, the median and the upper quartile.

When I ask you the obvious question now give me the lower quartile, the median and the upper quartile in these three boxes over here.

So, it's simple. All you need are those top quartile teachers.

What's interesting from now is I applied the quartile removal method.

And we hooked up with some people studying how much variation is there between teachers, between, say, the top quartile the very best and the bottom quartile.

We're actually splitting all the data into four groups this we'll call the first quartile, so I'll call it Q1 for the first quartile, maybe I'll do 1Q.

So, each quartile, since we have four of them has exactly two elements.

And then I compute a new data set where I just extract data in the range from the lower quartile to the upper quartile using this simple command over here.

For that I sorted the data and I computed the lower and upper quartile.

First, I want you to remove the outliers by only extracting data between the lower and upper quartile.

You did it. Professor Mitchell from Carnegie Mellon University with us today computed the quartile of this data sequence.

This one's called the median, the lower, and the upper quartile, and these guys are the ones being picked.

And in fact this range in between the upper quartile minus the lower one is called the interquartile range.

It turns out the number of data points make it well defined what the lower and upper quartile is.

After cleaning up and removing the points outside the quartile range, what do you think the new mean will be?

Okay, so you throw away the extremes, you arranged all points as before minus 99, 13, 17, 33, 1489, we find that these are the lower quartile and upper quartile, this happens to be the median these are the numbers that are average 13, 17 and 33.

And all the test cases we'll be using will have the property that the lower and upper quartile are well defined elements.

A top quartile teacher will increase the performance of their class based on test scores by over 10 percent in a single year.

That means that if the entire U.S., for two years, had top quartile teachers, the entire difference between us and Asia would go away.

This is the first quartile, or roughly a fourth of the trees, because the way you calculate it sometimes a tree ends up in one point or another.

About a fourth of the trees end up here, a fourth of the trees are between 14 and 21, a fourth are between 21 and it looks like 33, and then a fourth are in this quartile.

And I'm not asking whether there is in principle a variant of the method that can be used, but the way you've learned the method can we just go through both lists and independently in both lists remove the lower and the upper quartile?