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CHAPTER 4
CHAPTER 4
VARIABILITY
VARIABILITY
4.1 Introduction to Variability
4.1 Introduction to Variability
provides a quantitative measure of the differences between scores in a distribution and describes the degree to which the scores are spread out or clustered together
can also be viewed as measuring predictability, consistency, or diversity
describes the distribution of scores and measures how well an individual or group of scores represents the entire distribution
The Range
distance covered by the scores in a distribution, from smallest to largest
Xmax - Xmin
does not consider all the scores in the distribution so does not give an accurate description of the variability of the entire distribution
4.2 Defining Variance and Standard Deviation
4.2 Defining Variance and Standard Deviation
standard deviation: provides a measure of the average distance from the mean and describes whether the scores are clustered around the mean or scattered
square root of variance:
Find the mean
Calculate the deviation scores
Square deviation scores
Add all deviation scores
Divide by n-1 (sample) or by N(population)=variance
Take the square root of the variance to find the standard deviation
divide by n for the population and by n-1 for the sample
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