1 of 9

Measures of Spread

Variability

2 of 9

Standard Deviation

� 2

  • s = 1 ( x - x )

n-1

3 of 9

  • Larger standard deviation means larger spread

​

  • Smaller standard deviation means smaller spread

​

4 of 9

Example : Quiz scores

  • Given scores of 60, 70 and 80��To calculate s�
  • n=3
  • Mean = 70

5 of 9

Example : Quiz scores

  • Given scores of 60, 70 and 80 Get s
  • n=3 Mean = 70����� sum =200�s= =10

x

X-mean

(X-mean)2

60

-10

100

70

0

0

80

10

100

6 of 9

Variance

  • Standard deviation squared��
  • S2 =

7 of 9

Mean Absolute Deviation

  • MAD��
  • MAD =

8 of 9

Example : Quiz scores

  • Given scores of 60, 70 and 80 Get s
  • n=3 Mean = 70����� sum =20�MAD = = 6.33

x

X-mean

/X-mean/

60

-10

10

70

0

0

80

10

10

9 of 9

On Calculator

  • Enter Data in List ��STAT CALC 1- Var Stats�Sx��OR �2nd List ( STAT) MATH�stdDev(