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Measure of Dispersion

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• 1. 12.3 Measures of Dispersion
• 2. Range
The difference between the highest and lowest data values
Range = highest – lowest
• 3. Example 1
Find the range for a set of data:
A. 10, 20, 30, 40, 50
B. 84, 30, 90, 59, 67, 29
• 4. Standard Deviation
Dependent on all of the data items
Found by determining how each value deviates (or differs) from the mean
• 5. Computing the standard deviation for a data set
1. Find the mean of the data items.
2. Find the deviation of each data from the mean
data item – mean
3. Square each deviation
(data item – mean) 2
4. Sum the squared deviations
∑ (data item – mean) 2
• 6. Cont…
5. Divide the sum by n-1 where n represents the number of items.
∑ (data item – mean) 2
n-1
6. Take the square root of the answer.
√ ∑ (data item – mean) 2
n-1