Measures of Variability - PowerPoint PPT Presentation

1 / 12
About This Presentation
Title:

Measures of Variability

Description:

One basis of stereotyping is treating a group as if it were ... Standard Deviation is the square root of the variance. The smaller the number the less variation ... – PowerPoint PPT presentation

Number of Views:299
Avg rating:3.0/5.0
Slides: 13
Provided by: Horn82
Category:

less

Transcript and Presenter's Notes

Title: Measures of Variability


1
Measures of Variability
  • 02/02/2007

2
Summarizing Data
  • Central Tendency
  • Median, Mean
  • Variation and Diversity
  • Standard Deviation
  • Skewness

3
Importance of Variability
  • Experiences of U.S. women
  • Are they united by their similarities or divided
    by the differences?
  • One basis of stereotyping is treating a group as
    if it were totally represented by its mean,
    ignoring the diversity within the group

4
Index of Qualitative Variation
  • Nominal data
  • Index varies from 0.00 to 1.00
  • 0.00 ? no variation
  • 1.00 ? cases are evenly distributed
  • IQV K(1002 Sum(Pct2) / 1002(K-1)

5
Diversity for Two States
6
Range
  • Simplest measure of variation
  • Interval-ratio data
  • The difference between the highest (maximum) and
    lowest (minimum) scores in the distribution
  • Rather crude

7
Interquartile Range
  • Interval-ratio data
  • Difference between the lower and upper quartiles
    (Q1 and Q3).
  • Not very sensitive to extremes

8
Box Plot
9
Histogram
10
Variance and the Standard Deviation
  • Interval-ratio data
  • Variance is the average of the squared deviations
    from the mean
  • Standard Deviation is the square root of the
    variance
  • The smaller the number the less variation

11
Choosing the Proper Measure
  • No simple answer
  • Nominal
  • IQV
  • Ordinal
  • IQV (ignores rank order)
  • Range (sensitive to extremes)
  • IQR (ignores the tails)

12
Choosing a Measure
  • Interval
  • Range
  • IQV
  • IQR
  • Skewed distribution
  • Variance/Standard Deviation
  • Symmetric distribution
Write a Comment
User Comments (0)
About PowerShow.com