Determining Outliers

Determining Outliers

How do you verify a data point is an outlier?

• Arrange your data is numerical order

• Find the five number summary

• Use the five number summary to determine the IQR

• Multiply the IQR by 1.5

• Find the range of "good data".  Low =  $Q_1-1.5IQR$                       High =  $Q_3+1.5IQR$  

• Any data point that falls outside of this range is considered an outlier.

Poll

Yesterday in class we talked about a teacher taking some students to the park. Their ages were 1,1,2,2,2,3,4,4,9,10,10,62. Which age did we think was an outlier?

• 62

• 1

Is 62 really an outlier?

Let's walk through a students work to find out!

Multiple Select

Now that we know the range of good data, check all the ages that would be considered an outlier.

• 15

• 23

• Day old baby

• 34

• 3

Let's walk through another example together

The grades for the last quiz were 43, 62, 68, 73, 75, 79, 79, 82, 100. On the next slide, indicate which data point(s) may be outliers.

Poll

Here is the data again: 43, 62, 68, 73, 75, 79, 79, 82, 100

• 43

• 62

• 68

• 82

• 100

Results!?

Looks like we think 43 and 100 may be outliers. Let's confirm!

Step by Step

• Find Q₁ and Q₃

• Q₁ - 1.5IQR

• Q₃ + 1.5IQR

• Range of Good Data

It was close!

But the range of good data was 41.5 to 103.75. None of the grades would be considered an outlier!