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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We aren't going to spend a lot of time on this,
but there are a few things you should be aware of.