1. The 3 Ms of Central Tendency
Mean, Median, and Mode
Which one should you use?
Image retrieved 3/25/2012. From http://m-m.seebyseeing.net/

2. Why Does It Matter?
 You live in a town of 1,000 people where the
mean income is $25,000 and the median
income is about the same.
Retrieved from http://en.wikipedia.org/wiki/Damascus,_Virginia
4/7/2012

3. Why Does It Matter?
 Now the mean income is $1,023,976, but
the median income is still about $25,000.
Retrieved from http://genehoyas.com/ 4/7/2012

4. The Town of Millionaires
 It is a wonderful story about this
whole town of millionaires who
are so frugal they live in
ordinary homes. What a great
example of America!
 Why is this misleading?

5. Why Does It Matter?
 Most people in this town are still pretty
poor.
 The mean does not give a good picture of
the “typical” resident.
 This could be a big deal if the town loses
government services because of its
income level…but we will hope whoever is
in charge of those numbers does a little
better research.

6. Which M, M, & M would be best
for…
 The favorite movie of college students?

7. Which M, M, & M would be best
for…
 The favorite movie of college students?
 Mode: good for non-numerical data items
and for frequent occurrences.

8. Which M, M, & M would be best
for…
 The distances students in your class travel
to school.
Retrieved from
http://openclipart.org/detail/21980/toy-
car-by-nicubunu 4/7/2012

9. Which M, M, & M would be best
for…
 The distances students in your class travel
to school.
 Median: one student may live much further
than everyone else. When an outlier may
significantly influence the mean, we use
median.
Retrieved from
http://openclipart.org/detail/21980/toy-
car-by-nicubunu 4/7/2012

10. Which M, M, & M is best?
 The daily high temperature during a week in
July.
Retrieved from
http://activerain.com/blogsview/1205564/too-hot-to-blog-
dog-days-of-summer 4/7/2012

11. Which M, M, & M is best?
 The daily high temperature during a week in
July.
 Mean: since daily temperatures are not likely to
have an outlier, mean is best. When data have
no outlier, use mean.
Retrieved from
http://activerain.com/blogsview/1205564/too-hot-to-blog-
dog-days-of-summer 4/7/2012

12. Summary
 When data have no outliers, we typically
use mean.
 When data have outliers, we choose
median.
 When we are interested in the frequency
of particular values or we want to
summarize non-numeric data, we use
mode.

13. Measures of Central Tendency
 Go to the Khan Academy site whose web
address appears on the next slide and work with
the data to achieve the requested values for the
mean and median.
 This will help you determine the effect changes
in data have on those measures.
 Knowing this will help you figure out which M
works with the data best!

14. http://www.khanacademy.org/math/statistics/e/exploring_mean_and_median
 Below is a sample problem from the Khan
Academy website above.