1. Chapter 3: Averages and Variation
Section 1: Measures of Central Tendency

2. Measures of Central Tendency
A number that is meant to convey the idea of a center or a typical value for the data set.

3. Mode
·     The data value that occurs the most frequently for a set of data values
·     Some data sets have no mode
· Data sets may have more than one mode .

4. Median
·      The middle number for a collection of data values which are in order from least to greatest
·      the median is not influenced by extreme data values and therefore is a resistant measure

5. Mean
mean = =
sum of the data values
number of data values
population mean represented by
·     
sample mean represented by x
The mean is sensitive to outliers and therefore is not a resistant measure; it does not resist the effect of extreme values.

6. Examples Find the mean and median for the following sets of data.
# # #3

7. Relationship between mean and median
·     For a distribution which is skewed to the right, the mean will be greater than the median.
·     For a distribution which is skewed to the left, the mean will be less than the median.
For a bell shaped distribution, the mean and median will be equal.