# Introduction%20to%20Behavioral%20Statistics - PowerPoint PPT Presentation

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## Introduction%20to%20Behavioral%20Statistics

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