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!
