Central tendency mean activity1
Activity  Discussion  when is mean useful and when it is not
Estimated Time
Half period
Materials/ Resources needed
Illustration  Consider the wages of staff at a factory below:
Staff

1

2

3

4

5

6

7

8

9

10

Salary

15k

18k

16k

14k

15k

15k

12k

17k

90k

95k

Is the mean a good measure of central tendency for the data given above
Prerequisites/Instructions, if any
None
Multimedia resources
Website interactives/ links/ simulations/ Geogebra Applets
 https://en.wikipedia.org/wiki/Arithmetic_mean
 https://explorable.com/arithmeticmean
 http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Arithmetic_mean.html
Process (How to do the activity)
Share the example and ask students if the mean has been a good measure for central tendency
Developmental Questions (What discussion questions)
The mean salary for these ten staff is 30.7k. However, inspecting the raw data suggests that this mean value might not be the best way to accurately reflect the typical salary of a worker, as most workers have salaries in the $12k to 18k range. The mean is being skewed by the two large salaries. Therefore, in this situation we would like to have a better measure of central tendency. As we will find out later, taking the median would be a better measure of central tendency in this situation.
Evaluation (Questions for assessment of the child)
 Is the mean a good way to measure the average income of a citizen (per capita income)
 In what way do outliers make mean a measure that is not robust
Question Corner
Activity Keywords
To link back to the concept page central tendency