Measures of Variability

1
Measures of Variability

• Learning to calculate the
• Standard Deviations

2
Measures of Variability

• Using the Deviation formula to calculate the
  Standard Deviation.
• These formulas define what a standard deviation
  is but are cumbersome to calculate from.

3
Measures of Variability
4
Measures of Variability

• Using the Deviation formula to calculate the
  Standard Deviation.
• We can also calculate the SD using the deviation
  formula when we have grouped data.

5
Measures of Variability
6
Measures of Variability

• Calculator Formula
• The formula you will almost always use to
  calculate the SD is the calculator formula.

7
Measures of Variability
8
Measures of Variability

• Computing the Standard Deviation from Grouped
  data
• Need to correct for error due to grouping.
• Sheppards correction for grouping
• SD not the same, even with symmetrical
  distributions.
• If there are as many as 12-15 class intervals,
  the correction really makes little difference.

9
Measures of Variability

• Summary of Standard Deviation
• S.D. is the most used and most important measure
  of dispersion. Related to Variance.
• Arithmetic operations can be performed with it
• Most stable measure of dispersion.
• 68 of the scores fall 1 S.D.
• 95.4 of the scores fall 2 S.D.
• 99.74 of the scores fall 3 S.D.

10
Measures of Variability

• Relationships among measures of dispersion

11
Measures of Variability

• Next
• Measures of Skewness
• Measures of Kurtosis
• Standard Scores and other neat stuff