1. Measures of Spread
And
Outliers

2. Measures of Spread Range is a crude measure of spread
Other measures of spread:
Standard Deviation
Interquartile Range

3. Find the mean of the following set of data!
mean_____
How far away is each data point from the mean?

4. Standard Deviation
If the data is more condensed, each data point will be closer to the average. If the data is more spread out, each data point will be farther away from the average. Therefore: Smaller standard deviation = more consistent data!

5. You can use your calculator to find Standard Deviation!
STAT→CALC 1:1-Var Stats Sx = Standard Deviation!

6. Which student is more consistent?
Connie’s test scores
Oscar’s test scores
82, 82, 84, 84, 85, 85, 86
Mean –
Median –
Standard Deviation -
72, 76, 76, 84, 90, 94, 96
Mean –
Median –
Standard Deviation –
Which student is more consistent?

7. IQR: Q3 – Q1 Interquartile Range Interquartile Range (IQR) is easy!
It’s just the range between the quartiles!
IQR: Q3 – Q1

8. Example 1 Find the IQR (Interquartile Range) of the following data:
87, 7, 41, 50, 15, 220, 23, 99, 11, 45, 11, 61, 3, 39, 21

9. Example 2 Find the IQR (Interquartile Range) of the following data:
59, 27, 18, 78, 61, 91, 52, 34, 54, 93, 100, 87, 85, 82, 68

10. Choose the box and whisker plot that shows outliers!
Recall: Outliers are extreme pieces of data! How do we decide if a piece of data is extreme?
Use your calculator!
2nd→Y=
Turn Plot 1 On
ZOOM → 9:ZoomStat
Choose the box and whisker plot that shows outliers!

11. Does this data set have any outliers, and if so, what are they?
73, 56, 87, 65, 108, 65, 67, 58, 23, 56, 45 *Hint: Use the TRACE button on your calculator.