# Chapters 2-3

**Created:**2010-02-17

**Last Modified:**2011-07-14

- it's a way to summarize data
- it condenses the raw data into a more useful form
- allows for a quick visual interpretation of the data

used to see how data is spread over different categories

frequency in category/ total # of observations

used to stratify customers/products

use to influence decisions (show what you want to show)

affected by extreme values (outliers)

NOT affected by extreme values

^{th}position

i=(1/2)n

mean<median

mean-=median

mean>median

the value that occurs MOST OFTEN

not affected by extreme values

sum of squares/(n-1)

square root of sum of squares/(n-1)

difference between the largest and the smallest observations

=X

_{max}- X

_{min}

used to measure variation relative to the mean

measures scatter in the data relative to the mean

mean +or- 1 std dev contains about 68% of the values in the population or the sample

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