Introduction to Behavioral Statistics

- Standard Scores, Centiles and some other Odds

Ends

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.

Some Additional Measures of Dispersion

(Variability)

- Index of Dispersion
- A measure of dispersion of qualitative variables.
- Based on distinguishability of observations

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.,

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

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.

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.

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

Standard Scores

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.