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Introduction%20to%20Behavioral%20Statistics

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Introduction to Behavioral Statistics Standard Scores, Centiles and some other Odds & Ends Some Additional Measures of Dispersion (Variability) Coefficient of ... – PowerPoint PPT presentation

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Title: Introduction%20to%20Behavioral%20Statistics


1
Introduction to Behavioral Statistics
  • Standard Scores, Centiles and some other Odds
    Ends

2
Some Additional Measures of Dispersion
(Variability)
  • Coefficient of Variation -
  • A relative measure of dispersion
  • Used to compare distributions with different
    distributions.
  • Useful for comparing standard deviations of
    variables that involve different units of
    measurement.
  • The larger the CV, the larger the dispersion
    relative to the Mean.

3
Some Additional Measures of Dispersion
(Variability)
  • Index of Dispersion
  • A measure of dispersion of qualitative variables.
  • Based on distinguishability of observations

4
Centiles Test Norms
  • Introduction -
  • Knowing that you received a score of 70 on a
    test, provides you with no information about how
    well you did.
  • Knowing Rank Order helps, but there are problems.
  • Knowing the Mean provides still more information.
  • The centile provides an easy means to locate any
    given score in a distribution of scores and gets
    around the limitations of rank order.,

5
Centiles Test Norms
  • Centiles -
  • Introduction
  • If we know a score falls at the 20th percentile,
    we know that it is better than 20 of the scores
    and lower than 80 of the scores.
  • It is the point on the scale of measurement above
    which 80 of the scores fall and below which 20
    of the scores fall.
  • Computation

6
Centiles Test Norms
  • A way to give meaning to a score.
  • Makes the distribution rectangular
  • Since the Centile Rank is an Ordinal level
    measurement, they cannot be averaged.
  • Useful only for group computed on.

7
Standard Scores
  • A standard score is a raw score expressed in
    terms of standard deviation units from the mean.
  • This gives us a score which has a mean of 0
    (zero) and a SD of 1 (one).
  • We then know how many SDs any given score falls
    from the Mean.
  • Converting to standard score leaves skewness,
    kurtosis rank order unchanged.

8
Standard Scores
  • Other systems of Standard Scores
  • Navy system has mean of 50 and S.D. of 10
  • Air Force system has mean70 and SD10

9
Standard Scores
10
Next Probability the Normal Curve
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