1
Descriptive Statistics 3
4/6/2011
Announcements
•
Chapter 11 HW due Friday
–
Skip m. and n. (plots)
•
Bring calculators from now on
Central Tendency
•
Compute the mode, median, and mean for each
of these data sets:
Data set #1
Data set #2
i
Y
i
Y
1
5
1
1
2
5
2
4
3
5
3
5
4
5
4
5
5
5
5
10
Central Tendency
•
Data set #1
–
Mode = 5
–
Median = 5
–
Mean = 5
•
Data set #2
–
Mode = 5
–
Median = 5
–
Mean = 5
•
Clearly, the two data
sets are not identical
•
But central tendency
belies the truth
Other measures of dispersal
•
Standard Deviation and Variance
–
Measures of dispersion around the mean.

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2
Mean Absolute Deviation
Average distance of observations from mean.
1. Calculate mean.
2. Subtract the mean from each observations
l
value.
3. Take the absolute values of those.
4. Add up the differences.
5. Divide by n (number of observations).