Chapter 4: Measures of variability

Variability

* a quantitative distance measure based on the differences between scores

purpose of measure of variability

* describe the distribution
* measure how well an individual score represents the distribution

Range equation (continuos)

* (high X - Low x) +1

Range

* distance covered by the scores in a distribution
* smallest to highest value \`

Standard Deviation

* measure of the standard, or average, distance from the ,eam
* describes whether the scores are clustered closely around the mean or widely scattered

\

Steps to finding standard deviation for population

* sum up x
* sum up frequency (N)
* sum of x / N = mean
* get individual deviation (x-mean)
* square all values
* sum up all values of squared deviations (sum of squares (ss))
* get the population variance (ss / N)
* get the square root of above to get standard deviation

Steps to finding standard deviation for a sample

* sum up x
* sum up frequency (n)
* sum of x / n = mean
* get individual deviation (x-mean)
* square all values
* sum up all values of squared deviations (sum of squares (ss))
* get the population variance (ss / n-1)


* get the square root of above to get standard deviation

degrees of freedom

* number of scores in a sample that are independents
* n-1

When can mean change

* adding
* subtracting
* multiply
* divide

when can standard deviation change

* multiply
* divide

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High variability (graph wise)

graph with a lot of spread out results