Type of activity: In-class, small-group

Statistical topics: describing data numerically, effect of outliers, sample mean, sample median

Time needed: 10 minutes

Materials needed:

• An activity form (HTML Version) for the data collection and analysis

1. Ask students to break up into groups of 4 to 5 students.
2. Give one activity form to each student.
3. Ask the students to record the total number of "serious" significant others each person in the group has had.
4. Next, ask the students to calculate the sample mean and sample median from this initial data collection.
5. Then, have the students manipulate the data by multiplying the largest number from the original data set by ten.  Replace the largest original number with this new data point and leave all other original numbers the same.
6. Ask the students to recalculate the sample mean and sample median with the new data.
7. Ask the students to determine how the sample mean and sample median were affected by the presence of the outlier.
8. Make sure the students answer all the questions on the activity form.

After the students have completed the activity, the class should come back together as a group to discuss the purpose of the activity.  The instructor can initiate the discussion by asking the students what they learned in doing this activity.  Points to include:

• sample median is generally not affected by outliers.
• sample mean is affected by outliers.
• choice of using the mean or median to describe a data set depends on whether or not outliers are present.

Comments from others who have tried activity:  None.

Supplementary materials:  Activity Form: HTML Version